interfere with the drawing of air into the lungs. They may also result in permanent distortion of parts of the skeleton directly under the pressure. Other organs of the body cavity, as the stomach and intestines, may be forced downward, out of place, and in consequence do not perform their work properly.

Relation of Exercise. We have already seen that exercise results in the need of greater food supply, and hence a more rapid pumping of blood from the heart. With this, comes need of more oxygen to allow the oxidations which supply the greater energy used. Hence deeper breathing during time of exercise is a prime. necessity in order to increase the absorbing surface of the lungs.

Suffocation and Artificial Respiration. — Suffocation results from the shutting off of the supply of oxygen from the lungs. It may be brought about by an obstruction in the windpipe, by a lack of oxygen in the air, by inhaling some other gas in quantity, or by drowning. A severe electric shock may paralyze the nervous centers which control respiration, thus causing a kind of suffocation. In all the above cases, death may be prevented by recourse, in time, to artificial respiration. To accomplish this place the patient on his back with the head lower than the body; grasp the arms near the elbows and draw them upward and outward until they are stretched above the head, on a line with the body. By this means, the chest cavity is enlarged and an inspiration produced. To produce an expiration, carry the arms downward, and press them against the chest, thus forcing the air out of the lungs. This exercise, regularly repeated every few seconds, if necessary for hours, has been the source of saving many lives.

Effect of Alcohol and Tobacco on Respiration. It has been shown that alcohol tends to congest the membranes of the organs of respiration. This it does by relaxing the membranes of the throat and lungs.

"Those who have injured themselves with alcohol show less power of resistance against influences unfavorable to health, and are carried off by diseases which other people of the same age pass through safely, especially in cases of inflammation of the lungs." BIRCH-HIRSCHFELD.

"The action of alcohol upon the muscular walls of the arteries, which has been already more than once referred to, is especially important in the capillaries of the lungs. When they are dilated by the paralyzing effect of alcohol, their expansion reduces the

size of the air cells in the lungs and leaves less room for the air which the lungs need, so that less oxygen is supplied to the blood. When the capillaries are often or continuously distended in this way, their walls are likely to become permanently thickened, and the interchange of gases which normally takes place there, by which carbon dioxide passes from the blood while the purifying oxygen is taken into the blood, is impeded. Serious disease even may result, such as a peculiar and quickly fatal form of consumption found only among drinkers of alcoholic fluids.

"The throat, bronchial tubes, and lungs of a tobacco smoker are all liable to irritation by the poisonous smoke, and chronic inflammation is often caused. The nicotine of tobacco is a deadly poison, and in cigarettes there are often other poisons equally dangerous to health." MACY, Physiology.

"Dr. Legendre, a Paris physician, has recently published, for public distribution, a leaflet in which he says: 'Alcohol is a frequent cause of consumption by its power of weakening the lungs. Every year we see patients who attend the hospital for alcoholism come back after a period to be treated for consumption."" - London Lancet.

"An American medical writer (Journal of American Medical Association) points out the reason why the use of alcohol makes one liable to consumption. He mentions the use of alcohol among various other things which cause the natural vital resistance of the healthy body to be impaired. Among those other things mentioned with alcohol, which produce this impairment of vital resistance, are: 'Living in overcrowded, ill-ventilated houses, on damp soils, or insufficient clothing and outdoor exercise.'"HALL, Elementary Physiology.

Tobacco has a somewhat similar effect, besides causing a constant irritation of the diseased surfaces.

XXXIV. EXCRETION

Organs of Excretion.

All the life processes which take place in a living thing result ultimately in the formation of organic wastes within the body. This is the direct outcome of the processes we call oxidation. In the one-celled animals we find the outer layer of the body used to excrete or discharge waste materials. In some invertebrates, coiled tubes called nephidia are found, for the purpose of throwing off nitrogenous waste. In the vertebrate animals, the skin and kidneys perform this function, hence they are called the organs of excretion.

Laboratory Work on the Urino-genital System of the Frog. The organs of excretion and those of reproduction are closely connected in the frog, and are best studied together. In a male frog from which the digestive tract has been carefully removed, the kidneys may be found closely attached at the dorsal side of the body cavity. They are red-brown in color. How many are there? What is their general shape? The ovoid bodies, lying directly on the kidneys, are the spermaries. Notice the yellowish fingerlike bodies just anterior to the spermaries. These are the so-called fatty bodies; their function is not exactly known, though it is believed that they contain a reserve supply of food. Look along the outer edge of each kidney for tiny white tubes, the ureters, which connect each kidney with the cloaca. Just ventral to the cloaca is the urinary bladder, a large thin-walled biparted sac; this is also connected with the cloaca. (The bladder is frequently found in a collapsed condition. It is easy to cut it away unintentionally).

Draw the urino-genital system of the male frog (twice natural size), showing as many parts as you can.

In the female frog, a large part of the body cavity, especially at the breeding season, may be filled by the ovary; this contains a great number of black and white eggs, which may easily be seen through its very delicate walls. On each side of the body cavity, posterior to the ovary, are found two long and much-twisted tubes, the oviducts. In these tubes, the eggs receive a jellylike coat which protects them after they are laid. The oviducts are connected with the cloaca. The position of the kidneys, ureters, and bladder is practically the same as in the male frog.

Draw (twice natural size) the urino-genital system of the female frog, showing the ovary and oviduct on one side removed. Label all the parts shown.

Laboratory Work on the Kidney. - An idea of the internal structure of the kidney of man may be gained by examination of a sheep's kidney. Get the butcher to leave the mass of fat around the kidney. Of what use might this fat be? Notice, after removing the fat, that the kidney appears to be

The

closely wrapped in a thin coat of connective tissue; this is called the capsule. Remove the kidney from this capsule. Notice its color and shape. depression called the hilum is deeper than the corresponding region in the kidney bean. The hollow tube passing out from this region is called the ureter. Blood vessels also enter and leave the kidney at the hilum. Cut the kidney lengthwise into halves. Try to find the following regions: (1) The outer or cortical region; note its color; (2) The inner or medullary layer; this layer is provided with little projections; these are the pyramids of Malpighi, so called after their discoverer, Marcello Malpighi, a celebrated Italian physiologist; (3) the cavity or pelvis of the kidney. At the summit of each pyramid is a small opening through which escapes into the pelvis the secretion formed in the little tubules which make up the substance of the kidney. Draw a sheep's kidney, cut lengthwise, showing all the above points.

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G

The Human Kidney. - The description given above will apply almost exactly to the kidney of man except for the size. The human kidney is about four inches long, two and one half inches wide, and one inch in thickness. Its color is dark red. If you examine the structure of the medulla and cortex (see above) under the compound microscope, you will find these regions to be composed of a vast number of tiny branched and twisted tubules. The outer end of these tubules open into the pelvis; the inner end, in the cortex, forms a tiny closed sac. In each sac, the outer wall of the tube has grown inward and carried with it a very tiny artery. This artery breaks up into a mass of capillaries. These capillaries, in turn, unite to form a small vein as they leave the little sac. Each of these sacs with its contained blood vessels is called a glomerulus,

t

Diagram of kidney circulation, showing a glomerulus and tubule; a, artery bringing blood to part; b, capillary bringing blood to glomerulus; b', vessel continuing with blood to tubule; c, vein; t, tubule; G, glomerulus.

Wastes given off by the Blood in the Kidney. In the glomerulus the blood loses by osmosis, through the very thin walls of the capillaries, first, a considerable amount of water (amounting to nearly three pints daily); second, a nitrogenous waste material known as urea; third, salts and other waste organic substances, uric acid among them.

These waste products, together with the water containing them, are known as urine. The total amount of nitrogenous waste leaving the body each day is about twenty grams; this is nearly all accounted for in the urea passed off by the kidney, as urine is secreted in the kidney. It is passed through the ureter to the urinary bladder; from this reservoir it is passed out of the body, through a tube called the urethra. After the blood has passed through the glomeruli of the kidney it is purer than in any other place in the body, because, before coming to the kidney, the blood lost a large part of its burden of carbon dioxide in the lungs. After leaving the kidney it has lost much of its nitrogenous waste. So dependent is the body upon the excretion of its poisonous material that, in cases where the kidneys do not do their work properly, death may ensue within a few hours.

Effect on the Kidneys. It is said that alcohol is one of the greatest causes of disease in the kidneys. The forms of disease known as "fatty degeneration of the kidney" and "Bright's disease are both frequently due to this cause. The kidneys are the most important organs for the removal of nitrogenous waste. Alcohol unites more easily with oxygen than most other food materials, hence it takes away oxygen that would otherwise be used in oxidizing these foods. Imperfect oxidation of foods causes the development and retention of poisons in the blood which it becomes the work of the kidneys to remove. If the kidneys become overworked, disease will occur. Such disease is likely to make itself felt as rheumatism or gout, both of which are believed to be due to waste products (poisons) in the blood.

"Influence of Alcohol upon Excretion. If the waste substances constantly formed in the body are not promptly removed, they tend to poison the system. When the organism is at a high level of health, the breaking down of tissue by oxidation, which produces waste, goes on rapidly and vigorously. When this is retarded, as we have seen it to be when alcohol is introduced into