Chapter 22

INCUBATION

The differences in the process of reproduction in birds and mammals is frequently misunderstood. The laying of the bird's egg is not analogous to the birth of young in mammals.

The female, whether bird or beast, forms a true egg which must be fertilized by the male sperm cell before the offspring can develop. In the mammal, if fertilization does not occur, the egg which is inconspicuous, passes out of the body and is lost. If fertilized, it passes into the womb where the young develops through the embryonic stages, being supplied with nourishment and oxygen directly by the mother.

In the bird, the egg, fertilized or unfertilized, passes out of the body and, being of conspicuous size, is readily observed. The size of the egg is due to the supply of food material which is comparable with that supplied to the mammalian young during its stay in the mother's womb.

The reptiles lay eggs that are left to develop outside of the body of the mother, subject to the vicissitudes of the environment. The young of the bird, being warm blooded, cannot develop without more uniform temperature than weather conditions ordinarily supply. This heat is supplied by the instinctive brooding habit of the mother bird.

Fertility of Eggs

In a state of nature the number of eggs laid by wild fowl are only as many as can be covered by the female. These are laid in the spring of the year, and one copulation of the male bird is sufficient to fertilize the entire clutch. Under domestication, the hen lays quite indefinitely, and is served by the male at frequent intervals. The fertilizing power of the male bird extends over a period of about 15 days.

For most of my readers, it will be unnecessary to state that the male has no influence upon the other offspring than those which he actually fertilizes within this period. The belief in the influence of the first male upon the later hatches by another male is simply a superstition.

The domestic chicken is decidedly polygamous. The common rule is one male to 12 or 15 hens. I have had equally good results, however, with one male to 20 hens. In the Little Compton and South Shore districts, one male is used for thirty or even forty hens.

By infertile eggs is meant eggs in which the sperm cell has never united with the ovum. Such eggs may occur in a flock from the absence of the male, from his disinclination or physical inability to serve the hens, from the weakness or lack of vitality in the sperm cells, from his neglect of a particular hen, from lifelessness, or lack of vitality in the ovule, or from chance misses, by which some eggs fail to be reached by the sperm cells.

In practice, lack of sexual inclination in a vigorous looking rooster is very rare indeed. The more likely explanation is that he neglects some hens, or that the eggs are fertilized, but the germs die before incubation begins, or in the early stages of that process. The former trouble may be avoided by having a relay of roosters and shutting each one up part of the time. The latter difficulty will be diminished by setting the egg as fresh as possible, meanwhile storing them in a cool place. The other factors to be considered in getting fertile eggs, are so nearly synonymous with the problems of health and vitality in laying stock generally, that to discuss it here would be but a repetition of ideas.

In connection with the discussion of fertile eggs, I want to point out the fact that the whole subject of fertility as distinct from hatchability, is somewhat meaningless. The facts of the case are, that whatever factors in the care of the stock will get a large percentage fertile eggs, will also give hatchable eggs and vice versa. This is to be explained by the fact that most of the unfertile eggs tested out during incubation, are in reality dead germs in which death has occurred before the chick became visible to the naked eye. Such deaths should usually be ascribed to poor parentage, but may be caused by wrong storage or incubation. Likewise, it would not be just to credit all deaths after chicks became visible to wrong incubation, although the most of the blame probably belongs there.

Likewise, with brooder chicks, we must divide the credit of their livability in an arbitrary fashion between parentage, incubation, and care after hatching.

By the hatchability of eggs, we then mean the percentage of eggs set that hatch chicks able to walk and eat. By the livability of chicks, we mean the percentage of chicks hatched that live to the age of four weeks, after which they are subject to no greater death rate than adult chickens. By the livability of eggs, we mean the product of these two factors, i.e.: the percentage of chicks at four weeks of age based upon the total number of eggs set.

As before mentioned, the fertility of eggs bears fairly definite relation to the hatchability, so likewise the hatchability bears a relation to the livability of chicks. When poor hatches occur because of weak germs, as because of faulty incubation, this same injury to the chick's organism is carried over and causes a larger death among the hatched chicks.

Moreover, the relation between the two is not the same with all classes of hatches, but as hatches get poorer the mortality among the chicks increases at an accelerating rate. The following table gives a rough approximation of these ratios:

Per cent. of Per cent. of chick Per cent. of egg Hatchability. Livability. Livability. 100 100 100 90 95 85 80 88 70 70 84 50 60 72 43 50 55 27 40 40 16 30 24 7 20 10 2 10 2 1

These figures are based on incubator data. Eggs set under hens usually give a hatchability of 50 per cent. to 65 per cent., and livability of 70 per cent. to 80 per cent. The reason for the greater livability is that the real hatchability of the eggs is 70 per cent. to 75 per cent., and is reduced by mechanical breakage. The hatchability of eggs varies with the season. This variation is commonly ascribed to nature, it being stated that springtime is the natural breeding season, and therefore eggs are of greater fertility.

While there may be a little foundation for this idea, the chief cause is to be found in the manner of artificial incubation, as will be discussed in a later section of this chapter. The following table is given as the seasonable hatchability for northern states. This is based on May hatch of 50 per cent:

January 38 July 40 February 42 August 40 March 47 September 42 April 49 October 43 May 50 November 40 June 46 December 35

Most people have an exaggerated idea of the hen's success as a hatcher. I have a number of records of hen hatching with large numbers of eggs set, and they are all between 55 per cent. and 60 per cent. The reasons the hen does not hatch better are as follows:

First: Actual infertile eggs--usually, running about 10 per cent. in the best season of the year.

Second: Mechanical breakage.

Third: Eggs accidentally getting chilled by rolled to one side of the nests, or by the sick, lousy or crazy hens leaving the nests or standing up on the eggs.

Fourth: Eggs getting damp from wet nests, dung or broken eggs; thus causing bacterial infection and decay.

The last three causes are not present in artificial incubation. From my observation they cause a loss of 15 per cent. of the eggs that fail to hatch, when hens are managed in large numbers. This would properly credit our hens with hatches running from 70 per cent. to 75 per cent., which, for reasons later explained, is not equal to hatches under the best known conditions of artificial incubation.

The assumption that the hen is a perfect hatcher, even barring accidents and the inherited imperfection of the egg, is not, I think, in harmony with our general conception of nature. Not only are eggs under the hens subject to unfavorable weather conditions, but the hen, to satisfy her whims or hunger, frequently remains too long away from the eggs, allowing them to become chilled.

For directions of how to manage setting hens, consult the Chapter on "Poultry on the General Farm."

The Wisdom of the Egyptians.

Up to the present there have been just three types of artificial incubation that have proven successful enough to warrant our attention. These are:

First, the modern wooden-box-kerosene-lamp incubator which is seen at its best development in the United States.

Second, the Egyptian incubator of ancient origin, which is a large clay oven holding thousands of eggs and warmed by smouldering fires of straw.

Third, the Chinese incubator, much on the principle of the Egyptian hatchery, but run in the room of an ordinary house, heated with charcoal braziers and used only for duck eggs.

I have no accurate information on the results of the Chinese method, and as it is not used for hen eggs, we will confine our attention to the first two processes only.

I do not care to go into detail in discussing makes of box incubators, but I will mention briefly the chief points in the development of our present machines.

The first difficulties were in getting lamps, regulators, etc., that would give a uniform temperature. This now has been worked out to a point where, with any good incubator and an experienced operator, the temperature of the egg chamber is readily kept within the desired range.

These are two principal types of box incubators now in use. In the earliest of these, the eggs were heated by radiation from a tank of hot water. These machines depended for ventilation or, what is much more important, evaporation, upon chance air currents passing in and out of augur holes in the ends or bottom of the machine.

The second, or more modern type, warms the eggs by a current of air which passes around a lamp flue where, being made lighter by the expansion due to heat, the air rises, creating a draft that forces it into the egg chamber. There it is caused to spread by muslin or felt diaphragms so that no perceptible current of air strikes the eggs. This type is the most popular type of small incubator on the market. Its advantage will be more readily seen after the discussion of the principles of incubation.

Hazy tales of Egyptian incubators have gone the rounds of poultry papers these many years. More recently some accurate accounts from American travelers and European investigators have come to light, and as a result, the average poultry editor is kept busy trying to explain how such wonderful results can be obtained "in opposition to the well-known laws of incubation."

The facts about Egyptian incubators are as follows: They have a capacity of 50 to 100 thousand eggs, and are built as a single large room, partly underground and made of clay reinforced with straw. The walls are two or three feet thick. Inside, the main rooms are little clay domes with two floors.

The hatching season begins the middle of January and lasts three months. A couple of weeks before the hatching begins, the fireproof house is filled with straw which is set afire, thoroughly warming the hatchery. The ashes are then taken out and little fires built in pots are set around the outside of the big room. The little clay rooms with the double floors are now filled with eggs. That is, one is filled at a time, the idea being to have fresh eggs entering and chicks moving out in a regular order, so as not to cause radical changes in the temperature of the hatchery.

No thermometer is used, but the operator has a very highly cultivated sense of temperature, such as is possessed by a cheese maker or dynamite dryer. About the twelfth day the eggs are moved to the upper part of the little interior rooms where they are further removed from the heated floor. The eggs are turned and tested out much as in this country. They are never cooled and the room is full of the fumes and smoke of burning straw. The ventilation provided is incidental.

This is about the whole story save for results. The incubator men pay back three chicks for four eggs, and take their profits by selling the extra chicks that are hatched above the 75 per cent. This statement is in itself so astonishing and yet convincing, that to add that the hatch runs between 85 per cent. and 90 per cent. of all eggs set, and that the incubators of the Nile Delta hatch about 75,000,000 chicks a year seems almost superfluous. As for the explanation of the results of the Egyptian incubators compared with the American kerosene lamp type, I think it can best be brought about by a consideration in detail of the scientific principles of incubators.

Principles of Incubation.

HEAT.--To keep animal life, once started, alive and growing, we need: First, a suitable surrounding temperature. Second, a fairly constant proportion of water in the body substance. Third, oxygen. Fourth, food.

Now, a fertile egg is a living young animal and as such its wants should be considered. We may at once dispose of the food problem of the unhatched chick, by saying that the food is the contents of the egg at the time of laying, and as far as incubation is concerned, is beyond our control.

In consideration of external temperature in its relation to life, we should note: (A) the optimum temperature; (B) the range of temperature consistent with general good health; (C) the range at which death occurs. Just to show the principle at stake, and without looking up authorities, I will state these temperatures for a number of animals. Of course you can dispute the accuracy of these figures, but they will serve to illustrate our purpose:

External External External Internal Internal Optimum Healthful Fatal Optimum Fatal Point Range Range Point Range

Man 70 0 to 100 50 to 140 98 90 to 106

Dog 60 70 to 140 70 to 140 101 95 to 110

Monkey 90 30 to 140 30 to 140 101 95 to 108

Horse 80 20 to 120 20 to 120 99 95 to 105

Fowl 80 20 to 140 20 to 140 107 100 to 115

Newly hatched chick 90 70 to 100 40 to 120 108 100 to 115

Fertile egg at start of incubation 103 32 to 110 31 to 125 103 31 to 125

Egg incubated three days 103 98 to 105 80 to 118 103 95 to 118

Egg incubated eighteen days 103 75 to 105 50 to 118 106 98 to 116

This table shows, among other things, that we are considering in the chick not a new proposition to which the laws of general animal life do not apply, but merely a young animal during the process of growth to a point where its internal mechanism for heat control, has power to maintain the body temperature through a greater range of external temperature change.

In the cooling process that occurs after laying the living cells of the egg become dormant, and like a hibernating animal, the actual internal temperature can be subjected to a much greater range than when the animal is active. After incubation begins and cell activity returns, and especially after blood forms and circulation commences, the temperature of the chick becomes subject to about the same internal range as with other warm blooded animals.

In the case of fully formed animals, the internal temperature is regulated by a double process. If the external temperature be lowered, more food substance is combined with oxygen to keep up the warmth of the body, while, if the external temperature be raised, the body temperature is kept low by the cooling effects of evaporation. This occurs in mammals chiefly by sweating. Birds do not sweat, but the same effect is brought about by increased breathing. Now, the chick gradually develops the heat producing function during incubation, until towards the close of the period it can take care of itself fairly well in case of lowered external temperature. The power to cool the body by breathing is not, however, granted to the unhatched chick, and for this reason the incubating egg cannot stand excess of heat as well as lack of it.

The practical points to be remembered from the above are:

First: Before incubation begins, eggs may be subjected to any temperature that will not physically or chemically injure the substance.

Second: During the first few days of the hatch, eggs have no appreciable power of heat formation and the external temperature for any considerable period of time can safely vary only within the range of temperature at which the physiological process may be carried on.

Third: As the chick develops it needs less careful guarding against cooling, and must still be guarded against over-heating.

Fourth: It should be remembered, however, that eggs are very poor conductors of heat, and if the temperature change is not great several hours of exposure are required to bring the egg to the new temperature.

Temperature is the most readily observed feature about natural incubation and its control was consequently the first and chief effort of the early incubator inventors.

A great deal of experimental work has been done to determine the degree of temperature for eggs during incubation. The temperature of the hen's blood is about 105 to 107 degrees F. The eggs are not warmed quite to this temperature, the amount by which they fail to reach the temperature of the hen's body depending, of course, upon the surrounding temperature. 103 degrees F. is the temperature that has been generally agreed upon by incubator manufacturers. Some of these advise running 102 degrees the first week, 103 degrees the second, 104 degrees the third. As a matter of fact it is very difficult to determine the actual temperature of the egg in the box incubator. This is because the source of heat is above the eggs and the air temperature changes rapidly as the thermometer is raised or lowered through the egg chamber. The advice to place the bulb of the thermometer against the live egg is very good, but in practice quite variable results will be found on different eggs and different parts of the machine.

With incubators of the same make, and in all appearances identical, quite marked variation in hatching capacity has been observed in individual machines. Careful experimentation will usually show this to be a matter of the way the thermometer is hung in relation to the heating surfaces and to the eggs. Ovi-thermometers, which consists of a thermometer enclosed in the celluloid imitation of an egg, are now in the market and are perhaps as safe as anything that can be used.

As was indicated in the previous section greater care in temperature of the egg is necessary in the first half of the hatch. The temperature of 102 degrees F. as above given is, in the writer's opinion, too low for this portion of the hatch. An actual temperature of 104 degrees at the top of the eggs will, as has been shown by careful experimental work, give better hatches than the lower temperature.

Moisture and Evaporation.

The subject of the water content of the egg and its relation to life, is the least understood of poultry problems.

The whole study of the water content of the egg during incubation hangs on the amount of evaporation. Now, the rates of evaporation from any moist object is determined by two factors: vapor pressure and the rate of movement of the air past the object. As incubation is always carried on at the same temperature, the evaporating power of the air is directly proportioned to the difference in the vapor pressure of water at that temperature, and the vapor pressure of the air as it enters the machine. Thus, in order to know the evaporative power of the air, we have only to determine the vapor pressure of the air and to remember that the rate of evaporation is in proportion to this pressure, i.e.: when the vapor pressure is high the evaporation will be slow and the eggs remain too wet, and when the vapor pressure is low the eggs will be excessively dried out.

The reader is probably more familiar with the term relative humidity than the term vapor pressure, but as the actual significance of relative humidity is changed at every change in outside temperature, the use of this term for expressing the evaporating power of the air has led to no end of confusion.

The influence of air currents on evaporation is to increase it directly proportional with the rate of air movement. Thus, 10 cubic feet of air per hour passing through an egg chamber would remove twice as much moisture as would 5 cubic feet.

If the percentage of water in any living body be changed a relatively small amount, serious disturbances of the physiological processes and ultimately death will result. The mature animal can, by drinking, take considerable excess of water without danger, for the surplus will be speedily removed by perspiration and by the secretion from the kidneys. But the percentage of water in the actual tissues of the body can vary only within a narrow range of not more than three or four per cent. The chick in the shell is not provided with means of increasing its water content by drinking or diminishing it by excretion, but the fresh egg is provided with more moisture than the hatched chick will require, and the surplus is gradually lost by evaporation. This places the water content of the chick's body at the mercies of the evaporating power of the air that surrounds the egg during incubation.

To assume that these risks of uncertain rates of evaporation is desirable, is as absurd as to assume that the risks of rainfall are desirable for plant life. As the plants of a certain climate have become adapted to the amount of soil moisture which the climate is likely to provide, so the egg has by natural selection been formed with about as much excess of water as will be lost in an average season under the natural conditions of incubation. Plant life suffers in drought or flood, and likewise bird life suffers in seasons of abnormal evaporative conditions. This view is substantiated by the fact that the eggs of water fowl which are in nature incubated in damper places, have a lower water content than the eggs of land birds.

The per cent. of water contained in the contents of fresh eggs is about 74 per cent., or about 65.5 per cent, based on the weight, shell included. Unfortunately no investigations have been made concerning the per cent. of water present in the newly hatched chick.

Upon the subject of the loss of water for the whole period of incubation, valuable data has been collected at the Utah, Oregon and Ontario Experiment Stations.

In these tests we find that as a rule the evaporation of eggs under hens is less than in incubators. With both hens and incubators, the rate of evaporation is greatest at the Utah Station, which one would naturally expect from the climate. The eggs under hens at the Ontario Station averaged about 12 per cent. loss in weight, and those at the Utah Station about 15 per cent. At both stations, incubators without moisture ran several per cent. higher evaporation than eggs under hens. The conclusions at all stations were that the addition of moisture to incubators was a material aid to good hatches of livable chicks.

At Ontario the average evaporation ran from as low as 7 per cent. At Utah it reached as high as 24 per cent. Now as the entire loss of weight is loss of water, the solid contents remaining the same, and as the original per cent, of water contained in the egg (shell included) is only 65.5, the chicks of the two lots with the same amount of solid substance would contain water in the proportion of 58.5 to 41.5. Based on the weight of the chick, this would make a difference of water content of over 25 per cent.

That human beings or other animals could not exist with such differences in the chemical composition of the body, is at once apparent. In fact I do not believe that the chick can live under such remarkable circumstances. As I have picked the extreme cases in the series given, it is possible that these extremes were experimental errors, and as in the Utah data, no information is given as what happened to the chicks, I have no proof that they did live. But from the large number of hatches that were recorded below 9 per cent, and above 15 per cent., giving a variation of the actual water content in the chick's body of about 10 per cent., it is evident that chicks do hatch under remarkable physiological difficulties. One explanation that suggests itself is, that as there is considerable variation in evaporation of individual eggs due to the amount of shell porosity, and the chicks that hatch in either case may be the ones whose individual variations threw them nearer the normal.

By a further study from the Ontario data of the relation of the evaporation to the results in livable chicks, it can be readily observed that all good hatches have evaporation centering around the 12 per cent. moisture loss, and that all lots with evaporations above 15 per cent. hatch out extremely poor.

The general averages of the machines supplied with some form of moisture was 35 per cent. of all eggs set, in chicks alive at four weeks of age, while the machines ran dry gave only 20 per cent. of live chicks at a similar period.

Now, I wish to call attention to a further point in connection with evaporation. If the final measure of the loss of weight by evaporation were the only criterion of correct conditions of moisture in the chick's body, the hatches that show 12 per cent., or whatever the correct amount of evaporation may be, should be decidedly superior to those on either side. That they are better, has already been shown. But they are far from what they should be. An explanation is not hard to find. The correct content of moisture is not the only essential to the chick's well being at the moments of hatching, but during the whole period of incubation. Under our present system of incubation, the chick is immediately subject to the changing evaporation of American weather conditions. The data for that fact, picked at random, will be of interest. The following table gives the vapor pressure at Buffalo, N. Y., for twenty consecutive days in April:

April 1..................170 2..................130 3...................95 4..................103 5..................110 6..................106 7..................154 8..................183 9..................245 10.................311 11.................342 12.................286 13.................219 14.................248 15.................217 16.................193 17.................241 18.................306 19.................261 20.................204

Supposing a hatch to be started at the beginning of the above period, by the end of the first week, with the excessive evaporation, due to a low vapor pressure, the eggs would all be several per cent. below the normal water content; the fact that the next week was warm and rainy, and the vapor pressure rose until the loss was entirely counterbalanced, would not repair the injury, even though the eggs showed at the end of incubation exactly the correct amount of shrinkage. A man might thirst in the desert for a week, then, coming to a hole of water fall in and drown, but we would hardly accept the report of a normal water content found at the post-mortem examination as evidence that his death was not connected with the moisture problem.

The change of evaporation, due to weather conditions, is, under hens, less marked than in incubators. This is because there are no drafts under the hen, and because the hen's moist body and the moist earth, if she sets on the ground, are separate sources of moisture which the changing humidity of the atmosphere does not affect. Among about forty hens set at different times at the Utah Station and the loss of moisture of which was determined at three equal periods of six days each, the greatest irregularity I found was as follows: 1st period, 5.81 per cent; 2d period, 3.86 per cent; 3d period, 6.15 per cent. Compare this with a similar incubator record at the same station in which the loss for the three periods was 5.63, 9.18 and 2.15.

I think the reader is now in position to appreciate the almost unsurmountable difficulties in the proper control of evaporation with the common small incubator in our climate. It is little wonder that one of our best incubator manufacturers, after studying the proposition for some time, threw over the whole moisture proposition, and put out a machine in which drafts of air were slowed down by felt diaphragms and the use of moisture was strictly forbidden.

The moisture problem to the small incubator operator presents itself as follows: If left to the mercies of chance and the weather, the too great or too little evaporation from his eggs will yield hatches that will prove unprofitable. In order to regulate this evaporation, he must know and be able to control both vapor pressure and the currents of air that strike the eggs. Now he does not know the amount of vapor pressure and has no way of finding it out. The so-called humidity gauges on the market are practically worthless, and even were the readings on relative humidity accurately determined, they would be wholly confusing, for their effect of the same relative humidity on the evaporation will vary widely with variations of the out-of-door temperature.

If the operator knows or guesses that the humidity is too low, he can increase it by adding water to the room, or the egg chamber, but he cannot tell when he has too much, nor can he reduce the vapor pressure of the air on rainy days when nature gives him too much water. As to air currents he is little better off--he has no way to tell accurately as to the behavior of air in the egg chamber and changes in temperature of the heater or if the outside air will throw these currents all off, since they depend upon the draft principle.

Taking it all in all, the man with the small incubator had better follow the manufacturer's directions and trust to luck.

The writer has long been of the conviction that a plan which would keep the rate of evaporation within as narrow bounds as we now keep the temperature, would not only solve the problem of artificial incubation, but improve on nature and increase not only the numbers but the vitality or livability of the chicks. With a view of studying further the relations between the conditions of atmospheric vapor pressure, and the success of artificial incubation, I have investigated climatic reports and hatching records in the various sections of the world.

The following are averages of the monthly vapor pressures at four points in which we are interested:

Buffalo, St. Louis, San Fran- Cairo Month N.Y. Mo. cisco. Egypt January 87 98 311 279 February 81 94 310 288 March 138 224 337 287 April 171 283 332 311 May 301 423 317 328 June 466 550 345 365 July 546 599 374 413 August 496 627 382 435 September 429 506 389 372 October 285 327 342 365 November 271 225 285 321 December 143 133 243 397

A study of the extent of daily variations is also of interest. As a general thing they are less extreme in localities when the seasonal variations are also less. In Cairo, however, which has a seasonal variation greater than San Francisco, the daily variations during the hatching season are much less than in California. This is due to a constant wind from sea to land, and an absolute absence of rainfall, conditions for which Egypt is noted.

Nearness to a coast does not mean uniform vapor pressure, for with wind alternating from sea to land, it means just the opposite.

As will be readily seen the months in spring which give the best hatches, occupy a medium place in the humidity scale. The fact that both hens and machines succeed best in this period, is to me very suggestive of the possibility that with an incubator absolutely controlling evaporation, much of the seasonal variation in the hatchability would disappear.

The uniform humidity of the California coast is shown in the above table. This is not inconsistent with the excellent results obtained at Petaluma.

The Egyptian hatcher in his long experience has learned just about how much airholes and smudge fire are necessary to get results. With these kept constant and the atmosphere constant, we have more nearly perfect conditions of incubation than are to be found anywhere else in the world, and I do not except the natural methods. The climatic conditions of Egypt cannot be equaled in any other climate, but as will be shown in the last section of this chapter, their effect can be duplicated readily enough by modern science and engineering.

Mr. Edward Brown, who was sent over here by the English Government to investigate our poultry industry, was greatly surprised at our poor results in artificial incubation. Compared with our acknowledged records of less than 50 per cent. hatches, he quotes the results obtained in hatching 18,000 eggs at an English experiment station as 62 per cent. I have not obtained any data of English humidity, but it is undoubtedly more uniform than the eastern United States.

Ventilation--Carbon Dioxide.

The last of the four life requisites we have to consider is that of oxygen. The chick in the shell, like a fish, breathes oxygen which is dissolved in a liquid. A special breathing organ is developed for the chick during its embryonic stages and floats in the white and absorbs the oxygen and gives off carbon dioxide. The amount of this breathing that occurs in the chick is at first insignificant, but increases with development. At no time, however, is it anywhere equal to that of the hatched chicks, for the physiological function to be maintained by the unhatched chicks requires little energy and little oxidation.

Upon the subject of ventilation in general, a great misunderstanding exists. Be it far from me to say anything that will cause either my readers or his chickens to sleep less in the fresh air, yet for the love of truth and for the simplification of the problem of incubation, the real facts about ventilation must be given.

In breathing, oxygen is absorbed and carbon dioxide and water vapor are given off. It is popularly held that abundance of fresh air is necessary to supply the oxygen for breathing and that carbon dioxide is a poison. Both are mistakes. The amount of oxygen normally in the air is about 20 per cent. Of carbon dioxide there is normally three hundredths of one per cent. During breathing these gasses are exchanged in about equal volume. A doubling or tripling of carbon dioxide was formerly thought to be "very dangerous." Now, if the carbon dioxide were increased 100 times, we would have only three per cent., and have seventeen per cent. of oxygen remaining. This oxygen would still be of sufficient pressure to readily pass into the blood. We might breathe a little faster to make up for the lessened oxygen pressure. In fact such a condition of the air would not be unlike the effects of higher altitudes.

Some investigations recently conducted at the U.S. Experiment Station for human nutrition, have shown the utter misconception of the old idea of ventilation. The respiratory calorimeter is an air-tight compartment in which men are confined for a week or more at a time while studies are being made concerning heat and energy yielded by food products. It being inconvenient to analyze such an immense volume of air as would be necessary to keep the room freshened according to conventional ventilation standards, experiments were made to see how vitiated the air could be made without causing ill effects to the subject.

This led to a remarkable series of experiments in which it was repeatedly demonstrated that a man could live and work for a week at a time without experiencing any ill effects whatever in an atmosphere of his own breath containing as high as 1.86 per cent. of carbon dioxide, or, in other words, the air had its impurity increased 62 times. This agrees with what every chemist and physiologist has long known, and that is that carbon dioxide is not poisonous, but is a harmless dilutant just as nitrogen. This does not mean that a man or animal may not die of suffocation, but that these are smothered, as they are drowned, by a real absence of oxygen, not poisoned by a fraction of 1 per cent. of carbon dioxide.

In the same series of experiments, search was made for the mysterious poisons of the breath which many who had learned of the actual harmlessness of carbon dioxide alleged to be the cause of the ill effects attributed to foul air. Without discussion, I will say that the investigators failed to find such poisons, but concluded that the sense of suffocation in an unventilated room is due not to carbon dioxide or other "poisonous" respiratory products, but is wholly due to warmth, water vapor, and the unpleasant odors given off by the body.

The subject of ventilation has always been a bone of contention in incubator discussions. With its little understood real importance, as shown in the previous section, and the greatly exaggerated popular notions of the importance of oxygen and imagined poisonous qualities of carbon dioxide, the confusion in the subject should cause little wonder.

A few years ago some one with an investigating mind decided to see if incubators were properly ventilated, and proceeded to make carbon dioxide determinations of the air under a hen and in an incubator. The air under the hen was found to contain the most of the obnoxious gas. Now, this information was disconcerting, for the hen had always been considered the source of all incubator wisdom. Clearly the perfection of the hen or the conception of pure air must be sacrificed. Chemistry here came to the rescue, and said that carbon dioxide mixed with water, formed an acid and acid would dissolve the lime of an egg shell. Evidently the hen was sacrificing her own health by breathing impure air in order to soften up the shells a little so the chicks could get out. Since it could have been demonstrated in a few hours in any laboratory, that carbon dioxide in the quantities involved, has no perceptible effect upon egg shells, it is with some apology that I mention that quite a deal of good brains has been spent upon the subject by two experiment stations. The data accumulated, of course, fails to prove the theory, but it is interesting as further evidence of the needlessness in the old fear of insufficient ventilation.

At the Ontario Station, the average amounts of carbon dioxide under a large number of hens was .32 of one per cent., or about ten times that of fresh air, or one-sixth of that which the man breathed so happily in the respiratory calorimeter. With incubators, every conceivable scheme was tried to change the amount of carbon dioxide. In some, sour milk was placed which, in fermenting, gives off the gas in question. Others were supplied with buttermilk, presumably to familiarize the chickens with this article so they would recognize it in the fattening rations. In other machines, lamp fumes were run in, and to still others, pure carbon dioxide was supplied. The percentage of the gas present varied in the machines from .06 to .58 of one per cent. The results, of course, vary as any run of hatches would. The detailed discussion of the hatches and their relation to the amount of carbon dioxide as given in Bulletin 160 of the Ontario Station, would be unfortunately confusing to the novice, but would make amusing reading for the old poultryman. Speaking of a comparison of two hatches, the writer, on page 53 of the bulletin says, "The increase in vitality of chicks from the combination of the carbon dioxide and moisture over moisture only, amounting, as it does, to 4.5 per cent. of the eggs set, seems directly due to the higher carbon dioxide content." I cannot refrain from suggesting that if my reader has two incubators, he might set up a Chinese prayer machine in front of one and see if he cannot in like manner demonstrate the efficacy of Heavenly supplications in the hatching of chickens.

The practical bearing of the subject of ventilation in the small incubator is almost wholly one of evaporation. The majority of such machines are probably too much ventilated. In a large and properly constructed hatchery, such as is discussed in the last section of this chapter, the entire composition of the air, as well as its movement, is entirely under control. Nothing has yet been brought to light that indicates any particular attention need be given to the composition of such air save in regard to its moisture content, but as the control of this factor renders it necessary that the air be in a closed circuit, and not open to all out-doors, it will be very easy to subject the air to further changes such as the increasing oxygen, if such can be demonstrated to be desirable.

Turning Eggs.

The subject of turning eggs is another source of rather meaningless controversy. Of course, the hen moves her eggs around and in doing so turns them. Doubtless the reader, were he setting on a pile of door knobs as big as his head, would do the same thing. As proof that eggs need turning, we are referred to the fact that yolks stick to the shell if the eggs are not turned. I have candled thousands of eggs and have yet to see a yolk stuck to the shell unless the egg contained foreign organism or was several months old. However, I have seen hundreds of blood rings stuck to the shell. Whether the chick died because the blood rings stuck or whether the blood rings stuck because the chicken died I know not, but I have a strong presumption that the latter explanation is correct, for I see no reason if the live blood ring was in the habit of sticking to the shell, why this would not occur in a few hours as well as in a few days.

In the year 1901 I saw plenty of chicks hatched out in Kansas in egg cases, kitchen cupboards and other places where regular turning was entirely overlooked.

Mr. J.P. Collins, head of the Produce Department of Swift & Co., says that he was one time cruelly deserted in a Pullman smoker for telling the same story. The statement is true, however, in spite of Mr. Collins' unpleasant experience. Texas egg dealers frequently find hatched chickens in cases of eggs.

Upon the subject of turning eggs the writer will admit that he is doing what poultry writers as a class do on a great many occasions, i.e.: expressing an opinion rather than giving the proven facts. In incubation practice it is highly desirable to change the position of eggs so that unevenness in temperature and evaporation will be balanced. When doing this it is easier to turn the eggs than not to turn them, and for this reason the writer has never gone to the trouble of thoroughly investigating the matter. But it has been abundantly proven that any particular pains in egg turning is a waste of time.

Cooling Eggs.

The belief in the necessity of cooling eggs undoubtedly arose from the effort to follow closely and blindly in the footsteps of the hen. With this idea in mind the fact that the hen cooled her eggs occasionally led us to discover a theory which proved such cooling to be necessary. A more reasonable theory is that the hen cools the eggs from necessity, not from choice. In some species of birds the male relieves the female while the latter goes foraging.

But there is no need to argue the question. Eggs will hatch if cooled according to custom, but that they will hatch as well or better without the cooling is abundantly proven by the results in Egyptian incubators where no cooling whatever is practiced.

Searching for the "Open Sesame" of Incubation.

The experiment station workers have, the last few years, gone a hunting for the weak spot in artificial incubation. Some reference to this work has already been made in the sections on moisture and ventilation. Before leaving the subject I want to refer to two more efforts to find this key to the mystery of incubation and in the one case at least correct an erroneous impression that has been given out.

At the Ontario Station a patent disinfectant wash called "Zenoleum" was incidentally used to deodorize incubators. Now, for some reason, perhaps due to the belief that white diarrhoea was caused by a germ in the egg, this idea of washing with Zenoleum was conceived to be a possible solution of the incubator problem. In the numerous experiments at that station in 1907 Zenoleum applied to the machine in various ways was combined with various other incipient panaceas and at the end of the season the results of the various combinations were duly tabulated. The machine with buttermilk and Zenoleum headed the list for livable chicks.

For reasons explained in the chapter on "Experiment Station Work," the idea of contrasting the results of one hatch with one sort with the average results of many hatches of another sort is very poor science. Feeling that the Station men would hardly be guilty of expressing as they did in favor of such a method without better reason, I very carefully went over the results and compared all machines using Zenoleum with all machines without it. The results in favor of Zenoleum were less marked but still perceptible. I was somewhat puzzled, as I could see no rational explanation of the relation between disinfecting incubator walls and the hatchability of the chick in its germ-proof cage. Finally I hit upon the scheme of arranging the hatches by dates and the explanation became at once apparent. The hatching experiments had extended from March to July, but the Zenoleum hatches were grouped in April and early in May, when, as one would expect from weather conditions, all hatches were running good. After allowing for this error Zenoleum appeared as harmless and meaningless as would the Attar of Roses.

The second link after the missing link of incubation to which I wish to call your attention also occurred at the Ontario Station. The latter case, however, is happier in that no unwarranted conclusions were drawn and that an interesting bit of scientific knowledge was added to the world's store. The conception to be tested was an offshoot from the carbon dioxide theory. You will remember at the Utah Station the idea was that carbon dioxide was to dissolve the shell so the chick could break out easier.

At the Guelph Station the conception was that the carbon dioxide might dissolve the lime of the shell for the chick to use in "makin' hisself." As an egg could not be analyzed fresh and then hatched, a number were analyzed from the same hens and others from those hens were then incubated with the various amounts of carbon dioxide, buttermilk, Zenoleum, and other factors. The lime content of the contents of the fresh egg averaged about .04 grams. At hatching time the lime in the chick's body averaged about .20 grams and was always several times as great as the maximum of the eggs.

Clearly calcium phosphate of the chick's bones is made by the digestion of the calcium carbonate from the shell and its combination with the phosphorus of the yolk. Certainly a remarkable and hitherto unexplained fact. The amount of lime required is not great enough, however, to materially weaken the shell, but, of course, the process is vital to the chick as bones are quite essential to his welfare, but it is an "inside affair" of which the three-tenths of one per cent of carbon dioxide incidentally present under the hen is entirely irrelevant.

A further observation made by the investigator is that the chicks which obtained the lowest amount of lime were abnormally weak. As long as we are powerless to aid the chick in digesting lime this fact, like the other, belongs in the field of pure, rather than applied science. I think that we are safe in saying that the weakness caused the shortage of lime rather than vice versa; if the writer remembers runts in other animals are usually a little short of bone material.

The chemist of the station is to be given special credit for not jumping at conclusions. In the summary of this work he states: "There is apparently no connection between the amount of lime absorbed by the chick and the amount of carbon dioxide present during incubation."

The Box Type of Incubator In Actual Use.

Although the fact is not so advertised and frequently not recognized even by the makers, the success of existing incubators is directly proportional to the extent with which they control evaporation. In order to show this I have only to call attention briefly to two or three of the most successful types of incubators on the market.

Let me first repeat that evaporation increases with increased air currents and with decreased vapor pressure. Now, the vapor pressure undergoes all manner of changes with the passing of storm centers and the changes of prevailing winds. But there is a general tendency for vapor pressure to increase with increase in outside temperature. Now, the movement of air in all common incubators depends upon the draft principle and the greater the difference in machine temperature and outside temperature the greater will be this draft. Thus, we have two factors combining to cause variation in the rate of evaporation. The tendency for the rate of airflow to vary is diminished when a cellar is used for an incubator room, but the cellar does not materially remedy the climatic variation in vapor pressure.

The general tendency of incubators as ordinarily constructed, is to dry out the eggs too rapidly. With a view of counteracting this, water is placed in pans in the egg room. A surface of water exposed to quiet air does not evaporate as fast as one might think, as is easily shown by the fact that air above rivers, lakes and even seas is frequently far from the saturation point. The result of the moisture pan with a given current of air is that the vapor pressure is increased a definite amount, but by no means is it regulated or made uniform. Inasmuch as too much shrinking is the most prevalent fault in box incubators, the use of moisture is on the whole beneficial, but in hot, murky weather, with less circulation and higher outside vapor pressure, the moisture is overdone and the operator condemns the system.

The subject not being clearly understood and no means being available for vapor pressure determinations, the system results in confusion and disputes. When the felt diaphragm machine was brought into the market it was advertised as a no-moisture machine. The result of the diaphragm is that of choking off air movement and consequently reducing evaporation. This gives exactly the same results as the use of moisture, but the machine is easier to operate and seemed to do away with the vexatious moisture problem which, together perhaps, with some fancied resemblance of felt diaphragms to hen feathers, has resulted in the widespread use of this type of machine.

The latest effort along the lines of reducing evaporation is the sand tray machine that followed in the wake of the Ontario investigation. This device simply gives a greater evaporating surface to the water and hence a greater addition to the vapor pressure. The results in practice I had given me by a man who last year hatched sixty-five thousand chicks and as many more ducklings.

He said: "The sand tray early in the season gave the best hatches and most vigorous chicks we had, but later on things got too wet and the chickens drowned." No nicer demonstration of science in practice could be desired.

In the present-day incubator of either type we are wholly at the mercy of sudden climatic changes of vapor pressure. For the slower changes from season to season some control by greater and less amounts of supplied moisture, or by ventilator slides is available, but little understood and seldom practiced.

It will certainly be of interest to my readers to know the actual hatches obtained with the prevailing type of box incubator. By actual hatches we mean the per cent. of live chicks taken out of the machine to the per cent. of eggs put in. The ordinary published hatches, based on one per cent. of fertile hatches, are a delusion and a snare. When eggs are tested out many dead germs come out with them and the separation of microscopic dead germs from the infertile egg is, of course, impossible. Such padded and show hatching records do not interest us.

Where incubators are run on top of the ground I have found the results to be poor and to improve, the bigger and deeper and damper and warmer and less ventilated the cellar is made. The reason for this is plain. In such a cellar the vapor pressure of the air is not only greater but is less influenced by the shifting vapor pressure of the outside air. In a good cellar the operator, though his knowledge of the factors with which he deals is grievously deficient, learns, through long and costly experience, about what addition of moisture or about what rate of ventilation will give him the best results. In the room more subject to outside influences, the conditions are so constantly changing that uniformity of practice never gives uniform results, and hence the operator is without guidance, either intelligent or blind, and the results are wholly a product of chance.

As proof of my contention I may give results of a series of full season hatches for 1908, each involving several thousand eggs.

First, a state experiment station, the name of which I do not care to publish. Incubators kept in a cement basement which has flues in which fires were built to secure "ample ventilation." This caused a strong draft of cold, dry air, making the worst possible condition for incubation. The hatch for the season averaged 25 per cent. and was explained by lack of vitality in the stock.

Second, Ontario Agricultural College. A room above ground, moisture used in most machines and various other efforts being made to improve the hatches by a staff of half a dozen scientists. Results: Hatch 48 per cent.--incubator manufacturers call the experimenters names and say they are ignorant and prejudiced.

Third, Cornell University: dry ventilated basement representing typical conditions of common incubator practice of the country. Results: Hatch 52 per cent., results when given out commonly based on fertile eggs and every one generally pleased.

Fourth: One of the most successful poultrymen in New York State, who has, without knowing why, hit upon the plan of using a no-moisture type of incubator in a basement which is heated with steam pipes, which maintains temperature at 70 degrees and has a cement floor which is kept covered with water. Results: Hatch 59 per cent.

Fifth: As a fifth in such a series I might mention again the Egyptian machine with the uniform vapor pressure of the climate and the three chicks exchanged for four eggs.

While an official in the United States Department of Agriculture, I gathered data from original records of private plants covering the incubation of several hundred thousand eggs. Such information was furnished me in confidence as a public official and as a private citizen I have no right to publish that which would mean financial profit or loss to those concerned.

Of records where there were ten thousand or more eggs involved, the lowest I found was 44 per cent. and the highest, that mentioned as the fourth case above, or 59 per cent. The great majority of these records hung very closely around the 50 per cent. mark.

The following is a fair sample of such data. It is the record of hatching hen eggs for the first six months of 1908, at one of the largest poultry plants in America:

Eggs Chicks Per Cent. Month Set Hatched Hatched

January 4,213 1,585 37 2-3 February 6,275 2,339 33 3-4 March 17,990 6,993 38 1-3 April 18,819 10,265 54 1-2 May 24,458 14,438 59 June 13,100 6,614 55 ------ ------ ------ Total 84,855 42,234 50 p.c.

The Future Method of Incubation.

The idea of the mammoth incubator which would hatch eggs by the hundred thousand and a minimum of expense is the dream of the American incubator inventor. We have long had available such methods of insulation and regulating the supply of heat as would point to the practicability of such a dream.

The past efforts in this direction have fallen down for the following simple reason: All eggs were placed in a single big room with a view of the man's entering the room to take care of them. Contact with cold walls, the opening of doors, the hatching of chicks or introduction of fresh eggs set up air currents, the hot air rising and the cold air settling until great differences in temperature would be found in the room. No systematic regulation of evaporation was contemplated, as the principles at stake or the means of such regulation were unknown.

The attempt just referred to was made several years ago by one of the most successful of incubator manufacturers and because of his failure other inventors were inclined to steer clear of the proposition. Meanwhile the need of such an incubator has grown enormously. At the time that above effort was made no duck ranch existed whose annual production ran over thirty or forty thousand ducklings, whereas we now have several in the one hundred thousand class.

Much more remarkable has been the growth of the day-old chick business. The discovery that newly hatched chicks could be successfully shipped hundreds of miles with less loss than shipping eggs for hatching, has resulted in a few years' time in the growth of hatcheries of considerable size where chicks are hatched by means of common incubators. Still another opportunity for the use of large hatcheries has been by the growth of poultry communities. There are other communities besides those mentioned in this book which would amply support public hatcheries. If half the poultry growers of Lancaster County, Pa., were to be prevailed upon to patronize a public hatchery, the county would support between fifteen and twenty 100,000 egg incubators. Any of the numerous trolley centers in Indiana, Ohio and Southern Michigan would likewise be profitable locations for the establishment of public hatcheries.

The demand for the incubator of large capacity has, within the last year or so, brought two or three "mammoth" incubators into the market. The devices I now refer to consist of a row of box incubators which, instead of being heated by single lamps, are heated by continuous hot water pipes. This scheme effects a considerable saving in fuel cost and labor, but the bulkiness of construction and the woeful lack of evaporation control are still to be dealt with.

The writer now wishes briefly to describe the plan of construction and operation of a new type of hatchery, the success of which has recently been made feasible by inventions and technical knowledge hitherto unavailable. The plan of the hatchery is on that of a cold storage plant as far as insulation and general construction go. The eggs are kept in bulk in special cases which are turned as a whole and may rest on either of four sides. At hatching time the eggs are spread out in trays in a special hatching room, which is only large enough to accommodate chicks to the amount of one-sixth of the incubator capacity, for twice a week deliverings, or one-third if weekly deliveries are desired.

There are no pipes or other sources of heat in the egg chambers. All temperature regulation is by means of air heated (or cooled as the case may be) outside of the egg rooms and forced into the egg rooms by a motor driven cone fan, maintaining a steady current of air, the rate of movement of which may be varied at will. The air movement maintained will always be sufficiently brisk, however, to prevent an unevenness of temperature in different parts of the room.

So simple is this that the reader will doubtless wonder why it was not developed earlier. The reason is that air subject to the climatic influences will, with any forced draft sufficient to equalize temperature, result in a fatal rate of evaporation. Sprinkling the air has not generally been thought practical because of the notion that air must not be used in the egg chamber but once, which involved quite a waste of heat necessary in warming a large bulk of air and evaporating sufficient water. Moreover, no means has, in the past, been available for making a sufficiently accurate measurement of the evaporating power of the air.

The hair hygrometers commonly sold to incubator operators are known by scientists to be absolutely unreliable. The range between the wet and dry bulb thermometers was found in the Ontario experiments to give readings with and without fanning that varied 15 to 20 per cent. in relative humidity which, at the temperature of an egg chamber, would amount to a variation of three to four hundred of vapor pressure units, which, with the forced draught plan, would ruin a hatch of eggs in a few hours. The sling psychrometer as used by the U.S. Weather Bureau should, in the hands of an expert, give results making possible measurements accurate to two or three per cent. of relative humidity or forty to sixty units of vapor pressure. In contrast with these blundering instruments we now have available an instrument with which the writer has frequently determined vapor pressure accurately to within a range of two or three vapor pressure units and the instrument is capable of being constructed for even finer work.

As it is only by means of air with the moisture content absolutely controlled that the use of a large room becomes possible, we can now see why this type of hatching remained so long undeveloped. By means of such vapor pressure control the large egg chamber is not only feasible but the rate of evaporation at once becomes subject to the control of the operator and we achieve a perfection in artificial incubation hitherto unattained.

The means by which the air moisture is regulated is similar to that used in up-to-date cold storage plants where the air is made moist by sprinkling and dried with deliquescent salts. The regulation of vapor pressure, like that of temperature, may be by electrically moved dampers which switch a greater or less proportion of the incoming current to the sprinkler or dryer as the case may be. The ordinary incubator thermostat gives the necessary impulse for the control of the temperature dampers, while the instrument above referred to is used for the vapor pressure control.

As the entire air circuit is closed, the chemical composition of the air may also be regulated at will. This results in a reduction of the quantity of heat required to a minimum; in fact, with the incubator in full swing, the air will, at times, need cooling rather than warming.

The question of the cost of incubation by this method, or of profit of such a hatchery operated for the public is almost wholly one of the size of operations. Where sufficient eggs may be obtained and sufficient demand exists for the chicks to make it profitable to operate, the additional cost of hatching extra chicks will be insignificant compared with the present system.

The Egyptian poultryman gives four eggs for three chicks, but the American poultryman would be willing to give four eggs for one chick, as is shown by the fact that he sells eggs for from 1 to 3 cents apiece and buys day-old chicks for ten to fifteen cents. A plant with a seasonable capacity of 100,000 eggs has a basis to work upon something as follows:

With a fifty per cent. hatch and chicks at 10 cents each there would be a gross income of $5,000 annually. From this we must subtract for eggs at 2 cents each, $2,000. Salary for operator $1,000, wages for helper $300. Fuel, supplies and repairs $500. Cost of delivery and sales of chicks $200. This leaves a residue of $1,000, which would pay a 20 per cent. interest on the necessary investment of $5,000. Personally, I think this is about the minimum unit of hatching that would prove worth while as independent institutions.

Any increase in the percentage of the hatch would, of course, reduce the unit of size necessary for profitable operation. Upon a single poultry plant as a duck farm the cost of operation would be materially reduced, as the operator himself would take the place of the intelligent manager and the cost of gathering eggs and the delivery of the product would be eliminated.

The most profitable method of hatchery operation undoubtedly will be upon a plan analogous to what, in creamery operation, is called centralization. The success of this scheme depends upon the fact that transportation and agencies at country stores are relatively less important items of expense than plant construction and high salaries for skilled labor. A hatchery with a million capacity can be built and run at not more than twice the cost of one hundred-thousand plant and better men can be kept in charge of it. A portion of the saving will of course be expended in maintaining a system of buying eggs and selling chicks.

The material advantage of operating a hatchery in connection with a high-class egg handling and poultry packing establishment, or as one feature of a poultry community, is at once apparent, for the system of collecting the market produce will be utilized for gathering eggs and distributing chicks, each business helping the other.

The public hatchery also gives an excellent opportunity for the introduction of good stock among farmers who would be too shiftless to acquire it by ordinary methods.