Part 12

Typhoid Fever.--One of the most common germ diseases in this country and Europe is typhoid fever. This is a disease which is conveyed by means of water and food, especially milk, oysters, and uncooked vegetables. Typhoid fever germs live in the intestine and from there get into the blood and are carried to all parts of the body. A poison which they give off causes the fever so characteristic of the disease. The germs multiply very rapidly in the intestine and are passed off from the body with the excreta from the food tube. If these germs get into the water supply of a town, an epidemic of typhoid will result. Among the recent epidemics caused by the use of water containing typhoid germs have been those in Butler, Pa., where 1364 persons were made ill; Ithaca, N. Y., with 1350 cases; and Watertown, N. Y., where over 5000 cases occurred. Another source of infection is milk. Frequently epidemics have occurred which were confined to users of milk from a certain dairy. Upon investigation it was found that a case of typhoid had occurred on the farm where the milk came from, that the germs had washed into the well, and that this water was used to wash the milk cans. Once in the milk, the bacteria multiplied rapidly, so that the milkman gave out cultures of typhoid in his milk bottles. Proper safeguarding of our water and milk supply is necessary if we are to keep typhoid away.

Blood Poisoning.--The bacterium causing blood poisoning is another toxin-forming germ. It lives in dust and dirt and is often found on the skin. It enters the body through cuts or bruises. It seems to thrive best in less oxygen than is found in the air. It is therefore important not to close up with court-plaster wounds which such germs may have entered. It, with typhoid, is responsible for four times as many deaths as bullets and shells in time of battle. The wonderfully small death rate of the Japanese army in their war with Russia was due to the fact that the Japanese soldiers always boiled their drinking water before using it, and their surgeons always dressed all wounds on the battlefield, using powerful antiseptics in order to kill any bacteria that might have lodged in the exposed wounds.

Other Diseases.--Many other diseases have been traced to bacteria. Diphtheria is one of the best known. As it is a throat disease, it may easily be conveyed from one person to another by kissing, putting into the mouth objects which have come in contact with the mouth of the patient, or by food into which the germs have been carried. Another disease which probably causes more misery in the world than any other germ disease is syphilis. Hundreds of thousands of new-born babies die annually or grow up handicapped by deformities from this dread scourge. Syphilis and gonorrhea, both diseases of the same sort and contracted in the same manner, hand down to innocent wives and still more innocent children a heritage of disease "even unto the third and fourth generation." Grippe, pneumonia, whooping cough, and colds are believed to be caused by bacteria. Other diseases, as malaria, yellow fever, sleeping sickness, and probably smallpox, scarlet fever, and measles, are due to the attack of one-celled animal parasites. Of these we shall learn later in Chapter XV.

Immunity.--It has been found that after an attack of a germ disease the body will not soon be again attacked by the same disease. This immunity, of which we will learn more later, seems to be due to a manufacture in the blood of substances which fight the bacteria or their poisons. If a person keeps his body in good physical condition and lives carefully, he will do much toward acquiring this natural immunity.

Acquired Immunity.--Modern medicine has discovered means of protecting the body from some contagious diseases. Vaccination as protection against smallpox, the use of antitoxins (of which more later) against diphtheria, and inoculation against typhoid are all ways in which we may be protected against diseases.

Methods of fighting Germ Diseases.--As we have seen, diseases produced by bacteria may be caused by the bacteria being _directly_ transferred from one person to another, or the disease may obtain a foothold in the body from food, water, or by taking them into the blood through a cut or a wound or a body opening.

It is evident that as individuals we may each do something to prevent the spread of germ diseases, especially in our homes. We may keep our bodies, especially our hands and faces, clean. Sweeping and dusting may be done with damp cloths so as not to raise a dust; our milk and water, when from a suspicious supply, may be _sterilized_ or pasteurized. Wounds through which bacteria might obtain foothold in the body should be washed with some _antiseptic_ such as carbolic acid (1 part to 25 water), which kills the germs. In a later chapter we shall learn more of how we may cooperate with the authorities to combat disease and make our city or town a better place in which to live.[23]

Footnote 23: Teachers may take up parts or all of Chapter XXIV at this point. I have found it advisable to repeat much of the work on bacteria _after_ the students have taken up the study of the human organism.

REFERENCE BOOKS

ELEMENTARY

Hunter, _Laboratory Problems in Civic Biology_. American Book Company. Bigelow, _Introduction to Biology_. The Macmillan Company. Conn, _Bacteria, Yeasts, and Molds in the Home_. Ginn and Company. Conn, _Story of Germ Life_. D. Appleton and Company. Davison, _The Human Body and Health_. American Book Company. Frankland, _Bacteria in Daily Life_. Longmans, Green, and Company. Overton, _General Hygiene_. American Book Company. Prudden, _Dust and its Dangers_. G. P. Putnam's Sons. Prudden, _The Story of the Bacteria_. G. P. Putnam's Sons. Ritchie, _Primer of Sanitation_. World Book Company. Sharpe, _Laboratory Manual in Biology_, pages 123-132. American Book Company.

ADVANCED

Conn, _Agricultural Bacteriology_. P. Blakiston's Sons and Company. Coulter, Barnes, and Cowles, _A Textbook of Botany_, Vol. I. American Book Company. De Bary, _Comparative Morphology and Biology of the Fungi, Mycetozoa, and Bacteria_. Clarendon Press. Duggar, _Fungous Diseases of Plants_. Ginn and Company. Hough and Sedgwick, _The Human Mechanism_. Ginn and Company. Hutchinson, _Preventable Diseases_. Houghton, Mifflin and Company. Lee, _Scientific Features of Modern Medicine_. Columbia University Press. Muir and Ritchie, _Manual of Bacteriology_. The Macmillan Company. Newman, _The Bacteria_. G. P. Putnam's Sons. Sedgwick, _Principles of Sanitary Science and Public Health_. The Macmillan Company.

XII. THE RELATIONS OF PLANTS TO ANIMALS

_Problems.--To determine the general biological relations existing between plants and animals._ _(a) As shown in a balanced aquarium._ _(b) As shown in hay infusion._

SUGGESTIONS FOR LABORATORY WORK

_Demonstration of life in a "balanced" and "unbalanced" aquarium._--Determination of factors causing balance. _Demonstration of hay infusion._--Examination to show forms of animal and plant life. Tabular comparison between balanced aquarium and hay infusion.

Some Ways in which Plants affect Animals.--We have been studying the life of plants in order better to understand the life of animals and men. We have seen first that green plants play indirectly a tremendous part in man's welfare by supplying him with food. We have found that the colorless plants directly affected his welfare by causing disease, and by causing decay, thus making usable the nitrogen locked up in dead bodies of plants and animals, and by some even supplying nitrogen from the atmosphere. The dependence of animals upon plants has been shown and the interdependence of plants on animals has also been seen in cross-pollination and in the supply of raw food materials to plants by animals.

Study of a Balanced Aquarium.--Perhaps the best way for us to understand the interrelation between plants and animals is to study an aquarium in which plants and animals live and in which a balance has been established between the plant life on one side and animal life on the other. Aquaria containing green pond weeds, either floating or rooted, a few snails, some tiny animals known as water fleas, and a fish or two will, if kept near a light window, show this relation.

We have seen that green plants under favorable conditions of sunlight, heat, moisture, and with a supply of raw food materials, give off oxygen as a by-product while manufacturing food in their green cells. We know the necessary raw materials for starch manufacture are carbon dioxide and water, while nitrogenous material is necessary for the making of proteins within the plant. In previous experiments we have proved that carbon dioxide is given off by any living thing when oxidation occurs in the body. The crawling snails and the swimming fish give off carbon dioxide, which is dissolved in the water; the plants themselves, at all times, oxidize food within their bodies, and so must _pass off_ some carbon dioxide. The green plants in the daytime _use up_ the carbon dioxide obtained from the various sources and, with the water taken in, manufacture starch. While this process is going on, oxygen is given off to the water of the aquarium, and this free oxygen is used by the animals there.

But the plants are continually growing larger. The snails and fish, too, eat parts of the plants. Thus the plant life gives food to the animals within the aquarium. The animals give off certain nitrogenous wastes of which we shall learn more later. These materials, with other nitrogenous matter from the dead parts of the plants or animals, form part of the raw material used for protein manufacture in the plant. This nitrogenous matter is prepared for use by several different kinds of bacteria which first break the dead bodies down and then give it to the plants in the form of soluble nitrates. The green plants manufacture food, the animals eat the plants and give off organic waste, from which the plants in turn make their food and living matter. The plants give off oxygen to the animals, and the animals give carbon dioxide to the plants. Thus a balance exists between the plants and animals in the aquarium. Make a table to show this balance.

Relations between Green Plants and Animals.--What goes on in the aquarium is an example of the relation existing between all green plants and all animals. Everywhere in the world green plants are making food which becomes, sooner or later, the food of animals. Man does not feed to a great extent upon leaves, but he eats roots, stems, fruits, and seeds. When he does not feed directly upon plants, he eats the flesh of plant eating animals, which in turn feed directly upon plants. And so it is the world over; the plants are the food makers and supply the animals. Green plants also give a very considerable amount of oxygen to the atmosphere every day, which the animals may use.

The Nitrogen Cycle.--The animals in their turn supply much of the carbon dioxide that the plant uses in starch making. They also supply some of the nitrogenous matter used by the plants, part being given the plants from the dead bodies of their own relatives and part being prepared from the nitrogen of the air through the agency of bacteria, which live upon the roots of certain plants. These bacteria are the only organisms that can take nitrogen from the air. Thus, in spite of all the nitrogen of the atmosphere, plants and animals are limited in the amount available. And the available supply is used over and over again, perhaps in nitrogenous food by an animal, then it may be given off as organic waste, get into the soil, and be taken up by a plant through the roots. Eventually the nitrogen forms part of the food supply in the body of the plant, and then may become part of its living matter. When the plant dies, the nitrogen is returned to the soil. Thus the usable nitrogen is kept in circulation.[24]

Footnote 24: A small amount of nitrogen gas is returned to the atmosphere by the action of the decomposing bacteria on the ammonia compounds in the soil. (See figure of nitrogen cycle.)

Symbiosis.--We have seen that in the balanced aquarium the animals and plants, in a wide sense, form a sort of unconscious partnership. _This process of living together for mutual advantage is called symbiosis._ Some animals thus combine with plants; for example, the tiny animal known as the hydra with certain of the one-celled algae, and, if we accept the term in a wide sense, all green plants and animals live in this relation of mutual give and take. Animals also frequently live in this relation to each other, as the crab, which lives within the shell of the oyster; the sea anemones, which are carried around on the backs of some hermit crabs, aiding the crab in protecting it from its enemies, and being carried about by the crab to places where food is plentiful.

A Hay Infusion.--Still another example of the close relation between plants and animals may be seen in the study of a hay infusion. If we place a wisp of hay or straw in a small glass jar nearly full of water, and leave it for a few days in a warm room, certain changes are seen to take place in the contents of the jar; after a little while the water gets cloudy and darker in color, and a scum appears on the surface. If some of this scum is examined under the compound microscope, it will be found to consist almost entirely of bacteria. These bacteria evidently aid in the decay which (as the unpleasant odor from the jar testifies) is beginning to take place. As we have learned, bacteria flourish wherever the food supply is abundant. The water within the jar has come to contain much of the food material which was once within the leaves of the grass,--organic nutrients, starch, sugar, and proteins, formed in the leaf by the action of the sun on the chlorophyll of the leaf, and now released into the water by the breaking down of the walls of the cells of the leaves. The bacteria themselves release this food from the hay by causing it to decay. After a few days small one-celled animals appear; these multiply with wonderful rapidity, so that in some cases the surface of the water seems to be almost white with active one-celled forms of life. If we ask ourselves where these animals come from, we are forced to the conclusion that they must have been in the water, in the air, or on the hay. Hay is dried grass and may have been cut in a field near a pool containing these creatures. When the pool dried up, the wind may have scattered some of these little organisms in the dried mud or dust. Some may have existed in a dormant state on the hay and the water awakened them to active life. In the water, too, there may have been some living cells, plants and animals.

At first the multiplication of the tiny animals within the hay infusion is extremely rapid; there is food in abundance and near at hand. After a few days more, however, several kinds of one-celled animals may appear, some of which prey upon others. Consequently a struggle for life takes place, which becomes more and more intense as the food from the hay is used up. Eventually the end comes for all the animals unless some green plants obtain a foothold within the jar. If such a thing happens, food will be manufactured within their bodies, a new food supply arises for the animals within the jar, and a balance of life may result.

REFERENCE BOOKS

ELEMENTARY

Hunter, _Laboratory Problems in Civic Biology_. American Book Company. Sharpe, _A Laboratory Manual for the Solution of Problems in Biology_, pp. 133-138. American Book Company.

ADVANCED

Eggerlin and Ehrenberg, _The Fresh Water Aquarium and its Inhabitants_. Henry Holt and Company. Furneaux, _Life in Ponds and Streams_. Longmans, Green, and Company. Parker, _Biology_. The Macmillan Company. Sedgwick and Wilson, _Biology_. Henry Holt and Company.

XIII. SINGLE-CELLED ANIMALS CONSIDERED AS ORGANISMS

_Problems.--To determine:_ _(a) How a one-celled animal is influenced by its environment._ _(b) How a single cell performs its functions._ _(c) The structure of a single-celled animal._

LABORATORY SUGGESTIONS

_Laboratory study._--Study of paramoecium under compound microscope in its relation to food, oxygen, etc. Determination of method of movement, turning, avoiding obstructions, sensitiveness to stimuli. Drawings to illustrate above points. _Laboratory demonstration._--Living paramoecium to show structure of cell. Demonstration with carmine to show food vacuoles, and action of cilia. Use of charts and stained specimens to show other points of cell structure. Laboratory demonstration of fission.

The Simplest Plants.--We have seen that perhaps the simplest plant would be exemplified by one of the tiny bacteria we have just read about. A typical one-celled plant, however, would contain green coloring matter or chlorophyll, and would have the power to manufacture its own food under conditions giving it a moderate temperature, a supply of water, oxygen, carbon dioxide, and sunlight. Such a simple plant is the _pleurococcus_, the "green slime" seen on the shady sides of trees, stones, or city houses. This plant would meet one definition of a cell, as it is a minute mass of protoplasm containing a nucleus. It is surrounded by a wall of a woody material formed by the activity of the living matter within the cell. It also contains a little mass of protoplasm colored green. Of the work of the chlorophyll in the manufacture of organic food we have already learned. Such is a simple plant cell. Let us now examine a simple animal cell in order to compare it with that of a plant.

Where to find Paramoecium.--If we examine very carefully the surface of a hay infusion, we are likely to notice in addition to the scum formed of bacteria, a mass of whitish tiny dots collected along the edge of the jar close to the surface of the water. More attentive observation shows us that these objects move, and that they are never found far from the surface.

The Life Habits of Paramoecium.--If we place on a slide a drop of water containing some of these moving objects and examine it under the compound microscope, we find each minute whitish dot is a cell, elongated, oval, or elliptical in outline and somewhat flattened. This is a one-celled animal known as the _paramoecium_ or the slipper animalcule (because of its shape).

Seen under the low power of the microscope, it appears to be extremely active, rushing about now rapidly, now more slowly, but seemingly always taking a definite course. The narrower end of the body (the _anterior_) usually goes first. If it pushes its way past any dense substance in the water, the cell body is seen to change its shape temporarily as it squeezes through.

Response to Stimuli.--Many of these little creatures may be found collected around masses of food, showing that they are attracted by it. In another part of the slide we may find a number of the paramoecia lying close to the edge of an air bubble with the greatest possible amount of their surface exposed to its surface. These animals are evidently taking in oxygen by osmosis. They are breathing. A careful inspection of the jar containing paramoecia shows thousands of tiny whitish bodies collected near the surface of the jar. In the paramoecium, as in the one-celled plants, the protoplasm composing the cell responds to certain agencies acting upon it, coming from without; these agencies we call _stimuli_. Such stimuli may be light, differences of temperature, presence of food, electricity, or other factors of its surroundings. Plant and animal cells may react differently to the same stimulus. In general, however, we know that protoplasm is _irritable_ to some of these factors. To severe stimuli, protoplasm usually responds by _contracting_, another power which it possesses. We know, too, that plant and animal cells take in food and change the food to protoplasm, that is, that they _assimilate_ food; and that they may waste away and repair themselves. Finally, we know that new plant and animal cells are _reproduced_ from the original bit of protoplasm, a single cell.

The Structure of Paramoecium.--The cell body is almost transparent, and consists of semifluid protoplasm which has a granular grayish appearance under the microscope. This protoplasm appears to be bounded by a very delicate membrane through which project numerous delicate threads of protoplasm called _cilia_. (These are usually invisible under the microscope).

The locomotion of the paramoecium is caused by the movement of these cilia, which lash the water like a multitude of tiny oars. The cilia also send particles of food into a funnel-like opening, the _gullet_, on one side of the cell. Once inside the cell body, the particles of food materials are gathered into little balls within the almost transparent protoplasm. These masses of food seem to be inclosed within a little area containing fluid, called a _vacuole_. Other vacuoles appear to be clear; these are spaces in which food has been digested. One or two larger vacuoles may be found; these are the _contractile vacuoles_; their purpose seems to be to pass off waste material from the cell body. This is done by pulsation of the vacuole, which ultimately bursts, passing fluid waste to the outside. Solid wastes are passed out of the cell in somewhat the same manner. No breathing organs are seen, because osmosis of oxygen and carbon dioxide may take place anywhere through the cell membrane. The nucleus of the cell is not easily visible in living specimens. In a cell that has been stained it has been found to be a double structure, consisting of one large and one small portion, called, respectively, the _macronucleus_ and the _micronucleus_.