CHAPTER XX

MEDICAL AND PHYSIOLOGICAL METEOROLOGY

The starting point in any study of the physiological effects of weather and climate upon humanity is the remarkable fact that, on the hottest days of summer and the coldest of winter, in tropical deserts and amid polar snows, the temperature within the body of a healthy man remains constant to a fraction of a degree. There are slight temperature differences between different parts of the body; there is a periodic daily variation of about half a degree; and there are other slight changes, due to eating and exercise; but an internal temperature of about 98.6 degrees F. is maintained with little or no regard to fluctuations in the temperature of the air.

The body has often been compared to a building in which the temperature is regulated by a thermostat, but the comparison is not exact. The thermostat controls the temperature merely by regulating the combustion of fuel; and with the advent of mild weather we let the fires go out altogether. In the body the fires are always burning, the briskness with which they burn--or, to drop the metaphor, the rate at which bodily heat is generated--depending, above all, upon muscular activity, but also upon other causes. It is true that we possess a nervous mechanism, analogous to the thermostat, which tends to adjust the production of animal heat in such a manner as to offset the cooling effect of our environment; but this mechanism appears to be less important in maintaining our constant temperature than another, which regulates the loss of heat from the body. According to M. J. Rosenau:

“Heat is lost from the body chiefly in two ways; (1) by _heat transfer_, or loss by radiation, conduction, and convection; (2) by _evaporation_, chiefly by the evaporation of the water of perspiration. Pettenkofer and Voit estimated the loss of water by the lungs at 286 grams, and from the skin at from 500 to 1,700 grams daily. This will give some idea of the effects here concerned. The loss by heat transfer diminishes as the temperature of the surrounding air rises. The temperature of the body would rise when the atmospheric temperature goes above 70 degrees F. were not perspiration then secreted. So long as the perspiration can evaporate freely the heat production and heat loss are balanced. With a high humidity evaporation is lessened and the balance is maintained by rushing blood to the skin, which causes an elevation of the temperature of the surface, and thus the loss of heat by radiation, conduction, and convection is facilitated.”

Human sensations of temperature are paradoxical. We talk of being “hot” and “cold,” as if we belonged to the class of cold-blooded animals--the fishes and the reptiles--that actually undergo great variations of temperature, with variations in the temperature of their environment. We hear people say, for example, that they are most comfortable at a temperature of 65; yet we know that their temperature is always 98½, except just at the surface of the body.

The human body is, in fact, a poor thermometer. Our sensations do not register the temperature of the air, but they do, in a way, register the cooling power of the air, which depends upon temperature, humidity, and air movement, and they register, especially, changes in this cooling power, for within certain limits the body soon adapts itself to a constant rate of cooling, so as to lose any impression of heat or cold. When a steady outflow of heat from the body has been set up and the external cooling power is suddenly increased, we become conscious of a difference between the temperature at the surface of the body and the “blood temperature” beneath. The action of the nerves at the surface and the nerves underneath, under these circumstances, has been compared to that of a thermo-junction, in which an electric current is produced by differences of temperature. The rate of evaporation from the skin, also, has a marked effect upon our sensations of comfort and discomfort.

The common thermometer was long ago discredited as a means of measuring atmospheric comfort. Then, for a time, the wet-bulb thermometer had its day, and its indications were once published on a large scale in this country as representing the “sensible temperature,” or temperature that we actually feel. The wet-bulb thermometer is cooled by evaporation below the air temperature, except when the air is saturated with moisture, and may therefore give a rough indication of the temperature acquired by the skin when moistened with perspiration. The temperature of the skin is not, however, an accurate indication of our feelings of heat or cold, nor is it a satisfactory guide to the physiological effects of atmospheric conditions.

Several instruments have been devised for the purpose of measuring the cooling power of the air, to which the bodily mechanism must respond in order to maintain a uniform temperature within. One of these was invented nearly half a century ago by J. W. Osborne. A porous cylinder was filled with warm water, and an agitator, driven by clockwork, kept the water in the cylinder at uniform temperature at any given moment. The rate at which heat was lost from the wet surface of the cylinder was determined by a thermometer, having its bulb immersed in the water, and a stop watch. A different plan was adopted by A. Piche, in an instrument which he called the _deperditometer_, and which was supposed to imitate more closely the behavior of the body. A porous vessel is filled with water, the temperature of which is kept constantly at “blood heat” (98.6 degrees F.) by a gas jet provided with an automatic regulator. The amount of gas burned in a given time is then supposed to measure the cooling power of the atmosphere as it affects humanity. J. R. Milne’s _psuchrainometer_ is constructed on the same principle, but heat is supplied and measured electrically.

Among many other instruments of this class, one that now enjoys special favor is the _katathermometer_, devised by Prof. Leonard Hill, in England. This consists of a pair of large-bulbed spirit thermometers, one of which has its bulb covered with fine cotton mesh. To use the instrument, the bulbs are immersed in water at about 150 degrees F. until the spirit rises to the top of the thermometer tubes. The excess of water is then jerked off the wet bulb, and the other bulb is dried. The instruments are finally suspended in the air, and the rate of cooling from 110 to 100 degrees, or from 100 to 90 degrees, is taken with a stop watch. The dry-bulb measurements are supposed to show how fast the human body loses heat at its surface by radiation and convection, while the wet-bulb measurements also take account of evaporation.

In order to connect the readings of this device with human sensations, Hill and his collaborators have used the instrument under a great variety of atmospheric conditions, both indoors and out, and compared the readings with independent estimates of comfort and discomfort. On an ideal summer day the “wet kata” fell from 110 to 100 in 25 seconds, and the “dry kata” in 85 seconds. Indoors at the seaside in summer, under comfortable conditions, the readings were 50 seconds and 140 seconds, respectively. A large number of other readings, taken under different conditions in various parts of the word, have been published. The katathermometer is now used in both Great Britain and the United States in the study of ventilation problems, and has acquired a rather extensive literature. According to its inventor, “the heating and ventilation of rooms should be arranged so that the wet-bulb falls from 100 to 90 degrees in about one minute, and the dry-bulb in about three minutes.”

Regardless of the merits of these particular instruments, it is certain that the cooling power of the air--which is quite a different thing from the temperature of the air--is a very important factor in determining our comfort and our health. Within certain limits the body can easily adjust itself to changes in the cooling power of the air; within wider limits the adjustment is effected with difficulty, and we experience discomfort and possibly suffer in health; and finally there are extreme conditions, in either direction, to which adjustment is not possible; the internal temperature is then either lowered or raised, as the case may be, and a comparatively small change of this sort is fatal; i. e., death results by chilling or by heat stroke.

One interesting result of recent inquiries on this subject is the discovery that the bad effects of crowded, “stuffy” rooms are not generally due to impurities in the air, but to heat, humidity, and especially lack of air movement. It seems to be now demonstrated that there is no such thing as “crowd-poisoning,” and that the bad smells of confined places are no indication that the air is deleterious. Professor Hill, who has done more than anybody else to upset traditional ideas with regard to ventilation, tells us that “the deaths in the Black Hole of Calcutta, the depression, headache, etc., experienced in close rooms are alike due to heat stagnation; the victims of the Black Hole died of heat stroke.” Most recent writers on physiology also discredit the time-honored methods of testing the purity of the air by measuring the percentage of carbon dioxide it contains. The amount of this gas normally present in the free air is about three-hundredths of one per cent, but experiments have shown that thirty times this amount--a percentage higher than is found in the worst ventilated rooms--may be breathed for hours together without detrimental effects. A further departure from old-fashioned views is seen in the assertion of recent authorities that a deficiency of oxygen, unless far more pronounced than ever actually occurs in buildings, mines, etc., where the supply of this gas has been the subject of so much solicitude, has no physiological significance whatever. In support of this assertion it is pointed out that at mountain health resorts the concentration of oxygen out-of-doors is much less than that found in the worst ventilated rooms at sea-level. In mines an ample supply of oxygen may be positively dangerous, as favoring the occurrence of explosions. These were rare before the enactment of laws requiring a high percentage of oxygen in mine air.

Excessive dryness of the skin, which is a common cause of discomfort, is not very closely related to the humidity of the air. “In winter,” says Hill, “if there be a wind the rate of evaporation is so accelerated that the skin feels dry, because in order to check the loss of body heat the sweat glands are inactive and the blood vessels of the chilled skin are constricted.” There has been a great deal of discussion about the dry air of American buildings in winter, and startling figures have been adduced to show that the air of such buildings is dryer than that of deserts. So far as measurements of relative humidity go, this is perfectly true; but, as Dr. G. T. Palmer, of the New York State Commission on Ventilation, has pointed out, there is an important difference between dryness and “dryingness.” The latter depends upon the movement of the air, as well as the relative humidity. The circulation of the air in a desert is generally much more active than that of the air in a building with the windows shut, and therefore much more conducive to rapid evaporation. There are systems of ventilation in which the air is kept in steady and rapid motion, and it is probably only in such cases that the air of our heated houses can be compared to that of a desert. From the European point of view American buildings are notoriously overheated, but this is probably due to the fact that our hot summers--much hotter than those of Europe--have adapted us to a tropical climate.

It is natural to inquire whether the atmospheric conditions that affect the comfort of man do not also exercise a marked influence upon his muscular efficiency and his mental powers. This question has been answered in the affirmative by a number of ingenious writers, who have sought to establish definite quantitative relations between certain states of the atmosphere and the output of work in factories, the grades attained by school children, etc. Thus, Dr. Ellsworth Huntington, a well-known worker in this field, declares that the most favorable daily mean temperature for mental activity (the temperature being measured out-of-doors) is about 40 degrees F., and for physical activity about 60 degrees F. Contrary to the common opinion, he holds that our general efficiency is at low ebb in midwinter and fairly high in summer. Variability in temperature, within certain limits, he finds to be stimulating; equable temperature the reverse. He has drawn charts showing the distribution of what he calls “climatic energy”--i. e., the combination of certain weather factors supposed to control human efficiency--throughout the world, and other charts showing a more or less similar distribution of “civilization.” He has also made an ambitious attempt to interpret the history of mankind in terms of weather and climate.

Another fruitful worker along similar lines is Dr. Griffith Taylor, of Australia, who has made interesting studies of the control of settlement in his own country and elsewhere by temperature and humidity, and has introduced some novel graphic methods (“climographs”) for comparing climates with respect to their effects on humanity.

There has, in short, arisen a new school of climatologists whose aim is to develop exact mathematical formulæ whereby we shall be able to adjust the economic arrangements of mankind on an intelligent basis as regards climate. The success of their efforts is a question for the future to decide, but there is no doubt that their work is profoundly suggestive. These undertakings, it may be noted, bear a striking analogy to those of the present generation of agricultural meteorologists, who are applying climatic statistics to the problem of selecting crops and to the improvement of agricultural methods.

A certain number of specialists are engaged in studying the physiological effects of sunlight and other special kinds of solar radiation, the distribution of which varies greatly from place to place and from time to time, especially on account of differences in the selective absorption of such rays by the atmosphere. The chemical action of sunshine that causes sunburn--even at very low temperatures, as, for example, on high mountains--may have far-reaching effects on the human organism (as it certainly has on plants), and there is great need of collecting more data of “photochemical climate” than we now possess, in order that this subject may be thoroughly investigated. One of the few institutions in the world at which a large amount of work has been done in this line is the private observatory of Dr. C. Dorno, at Davos, the well-known health resort in the Alps. Dorno’s studies throw a good deal of light upon the therapeutic effects of sunshine in a mountain climate.

Many forms of dust in the atmosphere are capable of producing pronounced physiological and pathological effects. There is a long list of “dusty trades” in which the production of excessive dust has notoriously evil effects upon the health of workmen, leading especially to pulmonary diseases; sometimes to various kinds of poisoning. These harmful dusts are by no means confined to factories, mines, quarries, and the like. The air of the average city street abounds in them. Dr. J. G. Ogden states that 61 per cent of the dust found in the air of the New York subways consists of jagged splinters of steel, resulting from the wearing away of brake shoes, wheels, and rails.

The amount of danger to human health incurred through the presence of disease germs in the atmosphere has been the subject of much controversy. The present tendency is to regard this danger as very slight, under ordinary conditions. Thus, Dr. F. S. Lee writes:

“Evidence that disease germs pass through the air from room to room of a house or from a hospital to its immediate surroundings always breaks down when examined critically. It is indeed not rare now to treat cases of different infectious diseases in the same hospital ward. The one place of possible danger is in the immediate vicinity of a person suffering from a disease affecting the air passages, the mouth, throat, or lungs, such as a ‘cold’ or tuberculosis. Such a person may give out the characteristic microbe for a distance of a few feet from his body, not in quiet expiration, for simple expired air is sterile, but attached to droplets that may be expelled in coughing, sneezing, or forcible speaking. In this manner infection may, and probably does, occur, the evidence being perhaps strongest in the case of tuberculosis. But apart from this source there appears to be little danger of contracting an infectious disease from germs that float in the air.”

In regard to sewer gas, which still inspires so much dread in the popular mind, Dr. Lee says:

“Workmen in sewers are notoriously strong, vigorous, healthy men, with a low death rate among them. The specter of an invisible monster entering our homes surreptitiously from our plumbing pipes and sapping our lives and the lives of our children must be laid aside; we need no longer leave saucers of so-called ‘chlorides’ standing about our floors to neutralize in an impossible manner mysterious effluvia that do not exist; and when we return to our town houses in the autumn we may enter them with no fears that we are risking our lives by coming into a toxic, germ-infected, sewer gas-laden, deadly atmosphere.”

Present-day knowledge on the subject of infectious diseases discredits many ideas that once prevailed with regard to the effects of tropical climates on health. The remarkable results accomplished by vigorous sanitary measures in such places as Havana, the Isthmus of Panama and Guayaquil have aroused hopes--perhaps too sanguine--that eventually all parts of the tropics will be made healthful for the white race. In the Canal Zone the death rate of the large population of American men, women, and children is not higher than prevails in many cities of the United States; whereas, a generation ago, when the French were at work on the canal, the “climate” of this region was regarded as one of the most unhealthful in the world. Some authorities go so far as to assert that the deterioration in the general health and efficiency of white people in the tropics, so far as it actually occurs, is due entirely to preventable diseases. It would seem more rational, however, to assume that there are climates both in and out of the tropics which, on account of their heat, humidity, and other purely physical factors, are not so suitable for habitation for any race of humanity as others. How far acclimatization can go toward offsetting the effects of these atmospheric conditions is problematical.

The changes in the barometer that occur from day to day in regions where these changes are most pronounced are, on an average, not greater than those encountered in going from the bottom to the top of a good-sized hill, and are probably not directly of physiological importance. Certain European investigators, however, ascribe pathological effects to the minute and rapid barometric fluctuations--too small to be detected with an ordinary barometer--that occur, for example, when the foehn wind is blowing. Whether this is the cause, or a contributory cause, of “foehn-sickness,” of which one hears in Switzerland, is still uncertain.

The physiological effects of a rarefied atmosphere, as experienced in mountain climbing, ballooning, and aviation, are not yet well understood, despite the large amount of study that has been devoted to this subject. Recent views are thus summarized by Rosenau:

“The symptoms produced by a marked diminution in atmospheric pressure vary with circumstances. The effects are increased by cold, active muscular exertion, or improper clothing. The noticeable symptoms are increased rapidity of respiration and acceleration of the circulation, noises in the head and dizziness, impairment of the senses of sight, hearing, and touch, dullness of the intellectual faculties, and a strong desire to sleep. Sudden changes to a rarefied atmosphere cause syncope, weakness, dyspnœa, dizziness, and nausea. These threatening symptoms go by the name of ‘mountain sickness,’ Bert and Journet believe this condition is due to lack of oxygen, and the symptoms may, in fact, be relieved by adding oxygen to the air inspired. Kronecker concludes that mountain sickness is caused by a congestion of the lungs, impeding the flow of blood through them. Mosso and his followers attribute the physical disturbances of a reduced atmospheric pressure to the fact that the blood loses carbon dioxide more quickly than it loses oxygen, and they ascribe mountain sickness to this decrease of carbon dioxide in the blood. Cohnheim believes there is a concentration of the blood at high altitudes; in fact, insignificant increases have been found by competent observers.”

Divers and workers in caissons are subjected to high barometric pressure, amounting, at the maximum, to about 4½ atmospheres. According to Rosenau:

“The physiological effects of an increased atmospheric pressure are mainly due to an increase in the amount of atmospheric gases (especially nitrogen) which are taken up by the blood, and also to an increase in the chemical absorption of oxygen by the blood. The serious consequences usually result from too rapid decompression. As the pressure is released gas bubbles form. Gradual decompression gives a chance for the gas to escape from the lungs and be expelled without the production of bubbles.”

The health and comfort of many people seem to be affected, in a rather striking way, by the passage of the barometric depressions and areas of high pressure that alternate at intervals of a few days in the temperate zones. These effects should not be ascribed to changes of pressure, but rather to the accompanying changes in the other meteorological conditions. The late Dr. Weir Mitchell, who was a pioneer student of such phenomena, wrote of “a neuralgic belt, within which, as it sweeps along in advance of the storm, prevail in the hurt and maimed limbs of men, in the tender nerves and rheumatic joints, renewed torments called into existence by the stir and perturbation of the elements.” Victims of neuralgia and rheumatism are probably quite justified in regarding themselves as human barometers, capable of predicting with considerable accuracy the advent of stormy and rainy weather.

The fluctuations of temperature, humidity, and wind that attend the passage of barometric highs and lows would seem, in virtue of their effects on the heat-regulating mechanism of the body and consequent reactions upon the nervous system in general, to supply an ample explanation of the unpleasant symptoms above noted in the case of sensitive people; conditions to which the collective name of “cyclonopathy” has been given by European investigators, and which are extensively discussed in the works of Hellpach, Frankenhäuser, and Berliner. Some authorities have, however, invoked in this connection the possible effects of atmospheric electricity, and pointed to the extreme sensitiveness of many persons to the approach of thunderstorms; a condition which Dr. G. M. Beard named “astraphobia.” It is stated that the passage of a low-pressure area favors the emission of radioactive emanations from the ground, that the ionization of the atmosphere, and hence its electrical conductivity, is thus increased, and that the electric charge of the body is carried away more rapidly than usual. Here we enter upon a debatable subject, but one that thoroughly merits investigation. The human organism is the seat of various electrical phenomena, and these certainly cannot be independent of changes in the electrical state of the atmosphere.

Apart from possible direct effects of atmospheric electricity upon the human system, it has been suggested that electrical changes in the atmosphere affect the rate of reproduction of bacteria, and may therefore have some influence on the spread of infectious diseases.

The weather has many subtle influences upon the human mind, producing moods of cheerfulness and depression, and manifesting themselves in the records of the behavior of school children, in statistics of crime, insanity, suicide, drunkenness, etc. An interesting account of these manifestations is given by Dr. E. G. Dexter in his book “Weather Influences” (New York, 1904).

Finally, the aspect of meteorology that has thus far acquired the most definite shape in medical circles and given rise to the most coherent body of literature is Medical Climatology, which is designed to be applied in the climatic treatment of disease (climatotherapy). Thus many compilations have been made of the climatic statistics of health resorts, and these resorts have been classified with respect to their supposed climatic effects upon various diseases. From the point of view of the physical climatologist, the statistics found in such books seem, in general, both meager and ill adapted to bring out important features of the climates discussed; to say nothing of the fact that the whole subject of climatotherapy is fraught with controversy--whereof the history of the treatment of tuberculosis furnishes a shining example!