Now, just as the chyle was not fit to be immediately taken up by the

blood, but was passed through the mesenteric glands to be properly

worked over, so the lymph is carried to the lymphatic glands, where it

undergoes certain changes to fit it for being poured into the blood.

Nature, like a careful housekeeper, allows nothing to be wasted that

can be of any further service in the animal economy (Figs. 63 and 64).

The lymphatics unite to form larger and larger vessels, and at last

join the thoracic duct, except the lymphatics of the right side of the

head and chest and right arm. These open by the right lymphatic duct

into the venous system on the right side of the neck.

The whole lymphatic system may be regarded as a necessary appendage to

the vascular system (Chapter VII.). It is convenient, however, to treat

it under the general topic of absorption, in order to complete the

history of food digestion.

160. The Spleen and Other Ductless Glands. With the lymphatics may be

classified, for convenience, a number of organs called ductless or

blood glands. Although they apparently prepare materials for use in the

body, they have no ducts or canals along which may be carried the

result of their work. Again, they are called blood glands because it is

supposed they serve some purpose in preparing material for the blood.

The spleen is the largest of these glands. It lies beneath the

diaphragm, and upon the left side of the stomach. It is of a deep red

color, full of blood, and is about the size and shape of the palm of

the hand.

The spleen has a fibrous capsule from which partitions pass inwards,

dividing it into spaces by a framework of elastic tissue, with plain

muscular fibers. These spaces are filled with what is called the spleen

pulp, through which the blood filters from its artery, just as a fluid

would pass through a sponge. The functions of the spleen are not known.

It appears to take some part in the formation of blood corpuscles. In

certain diseases, like malarial fever, it may become remarkably

enlarged. It may be wholly removed from an animal without apparent

injury. During digestion it seems to act as a muscular pump, drawing

the blood onwards with increased vigor along its large vein to the

liver.

The thyroid is another ductless gland. It is situated beneath the

muscles of the neck on the sides of “Adam’s apple” and below it. It

undergoes great enlargement in the disease called goitre.

The thymus is also a blood gland. It is situated around the windpipe,

behind the upper part of the breastbone. Until about the end of the

second year it increases in size, and then it begins gradually to

shrivel away. Like the spleen, the thyroid and thymus glands are

supposed to work some change in the blood, but what is not clearly

known.

The suprarenal capsules are two little bodies, one perched on the top

of each kidney, in shape not unlike that of a conical hat. Of their

functions nothing definite is known.

Experiments.

The action produced by the tendency of fluids to mix, or become equally

diffused in contact with each other, is known as _osmosis_, a form of

molecular attraction allied to that of adhesion. The various physical

processes by which the products of digestion are transferred from the

digestive canal to the blood may be illustrated in a general way by the

following simple experiments.

The student must, however, understand that the necessarily crude

experiments of the classroom may not conform in certain essentials to

these great processes conducted in the living body, which they are

intended to illustrate and explain.

Illustration: Fig. 62.

Experiment 62. _Simple Apparatus for Illustrating Endosmotic Action._

“Remove carefully a circular portion, about an inch in diameter, of the

shell from one end of an egg, which may be done without injuring the

membranes, by cracking the shell in small pieces, which are picked off

with forceps. A small glass tube is then introduced through an opening

in the shell and membranes of the other end of the egg, and is secured

in a vertical position by wax or plaster of Paris, the tube penetrating

the yelk. The egg is then placed in a wine-glass partly filled with

water. In the course of a few minutes, the water will have penetrated

the exposed membrane, and the yelk will rise in the tube.”—Flint’s

_Human Physiology_, page 293.

Experiment 63. Stretch a piece of moist bladder across a glass tube,—a

common lamp-chimney will do. Into this put a strong saline solution.

Now suspend the tube in a wide mouthed vessel of water. After a short

time it will be found that a part of the salt solution has passed

through into the water, while a larger amount of water has passed into

the tube and raised the height of the liquid within it.

161. The Quantity of Food as Affected by Age. The quantity of food

required to keep the body in proper condition is modified to a great

extent by circumstances. Age, occupation, place of residence, climate,

and season, as well as individual conditions of health and disease, are

always important factors in the problem. In youth the body is not only

growing, but the tissue changes are active. The restless energy and

necessary growth at this time of life cannot be maintained without an

abundance of wholesome food. This food supply for young people should

be ample enough to answer the demands of their keen appetite and

vigorous digestion.

In adult life, when the processes of digestion and assimilation are

active, the amount of food may without harm, be in excess of the actual

needs of the body. This is true, however, only so long as active

muscular exercise is taken.

In advanced life the tissue changes are slow, digestion is less active,

and the ability to assimilate food is greatly diminished. Growth has

ceased, the energy which induced activity is gone, and the proteids are

no longer required to build up worn-out tissues. Hence, as old age

approaches, the quantity of nitrogenous foods should be steadily

diminished.

Experiment 64. Obtain a sheep’s bladder and pour into it a heavy

solution of sugar or some colored simple elixir, found at any drug

store. Tie the bladder carefully and place it in a vessel containing

water. After a while it will be found that an interchange has occurred,

water having passed into the bladder and the water outside having

become sweet.

Experiment 65. Make a hole about as big as a five-cent piece in the

large end of an egg. That is, break the shell carefully and snip the

outer shell membrane, thus opening the space between the outer and

inner membranes. Now put the egg into a glass of water, keeping it in

an upright position by resting on a napkin-ring. There is only the

inner shell membrane between the liquid white of the egg (albumen) and

the water.

An interchange takes place, and the water passes towards the

albumen. As the albumen does not pass out freely towards the water,

the membrane becomes distended, like a little bag at the top of the

egg.

162. Ill Effects of a too Generous Diet. A generous diet, even of those

who take active muscular exercise, should be indulged in only with

vigilance and discretion. Frequent sick or nervous headaches, a sense

of fullness, bilious attacks, and dyspepsia are some of the

after-effects of eating more food than the body actually requires. The

excess of food is not properly acted upon by the digestive juices, and

is liable to undergo fermentation, and thus to become a source of

irritation to the stomach and the intestines. If too much and too rich

food be persistently indulged in, the complexion is apt to become

muddy, the skin, especially of the face, pale and sallow, and more or

less covered with blotches and pimples; the breath has an unpleasant

odor, and the general appearance of the body is unwholesome.

An excess of any one of the different classes of foods may lead to

serious results. Thus a diet habitually too rich in proteids, as with

those who eat meat in excess, often over-taxes the kidneys to get rid

of the excess of nitrogenous waste, and the organs of excretion are not

able to rid the tissues of waste products which accumulate in the

system. From the blood, thus imperfectly purified, may result kidney

troubles and various diseases of the liver and the stomach.

163. Effect of Occupation. Occupation has an important influence upon

the quantity of food demanded for the bodily support. Those who work

long and hard at physical labor, need a generous amount of nutritious

food. A liberal diet of the cereals and lean meat, especially beef,

gives that vigor to the muscles which enables one to undergo laborious

and prolonged physical exertion. On the other hand, those who follow a

sedentary occupation do not need so large a quantity of food.

Brain-workers who would work well and live long, should not indulge in

too generous a diet. The digestion of heavy meals involves a great

expenditure of nervous force. Hence, the forces of the brain-worker,

being required for mental exertion, should not be expended to an

unwarranted extent on the task of digestion.

164. Effect of Climate. Climate also has a marked influence on the

quantity of food demanded by the system. Much more food of all kinds is

consumed in cold than in warm climates. The accounts by travelers of

the quantity of food used by the inhabitants of the frigid zone are

almost beyond belief. A Russian admiral gives an instance of a man who,

in his presence, ate at a single meal 28 pounds of rice and butter. Dr.

Hayes, the Arctic traveler, states from personal observation that the

daily ration of the Eskimos is 12 to 15 pounds of meat. With the

thermometer ranging from 60 to 70° F. below zero, there was a

persistent craving for strong animal diet, especially fatty foods.[24]

Illustration: Fig. 63.—Lymphatics and Lymphatic Glands of the Axilla.

The intense cold makes such a drain upon the heat-producing power of

the body that only food containing the largest proportion of carbon is

capable of making up for the loss. In tropical countries, on the other

hand, the natives crave and subsist mainly upon fruits and vegetables.

165. The Kinds of Food Required. An appetite for plain, well-cooked

food is a safe guide to follow. Every person in good health, taking a

moderate amount of daily exercise, should have a keen appetite for

three meals a day and enjoy them. Food should be both nutritious and

digestible. It is nutritious in proportion to the amount of material it

furnishes for the nourishment of the tissues. It is digestible in a

greater or less degree in respect to the readiness with which it yields

to the action of the digestive fluids, and is prepared to be taken up

by the blood. This digestibility depends partly upon the nature of the

food in its raw state, partly upon the effect produced upon it by

cooking, and to some extent upon its admixture with other foods.

Certain foods, as the vegetable albumens, are both nutritious and

digestible. A hard-working man may grow strong and maintain vigorous

health on most of them, even if deprived of animal food.

While it is true that the vegetable albumens furnish all that is really

needed for the bodily health, animal food of some kind is an economical

and useful addition to the diet. Races of men who endure prolonged

physical exertion have discovered for themselves, without the teaching

of science, the great value of meat. Hence the common custom of eating

meat with bread and vegetables is a sound one. It is undoubtedly true

that the people of this country, as a rule, eat meat too often and too

much at a time. The judicious admixture of different classes of foods

greatly aids their digestibility.

The great abundance and variety of food in this country, permit this

principle to be put into practice. A variety of mixed foods, as milk,

eggs, bread, and meat, are almost invariably associated to a greater or

less extent at every meal.

Oftentimes where there is of necessity a sameness of diet, there arises

a craving for special articles of food. Thus on long voyages, and

during long campaigns in war, there is an almost universal craving for

onions, raw potatoes, and other vegetables.

166. Hints about Meals. On an average, three meals each day, from five

to six hours apart, is the proper number for adults. Five hours is by

no means too long a time to intervene between consecutive meals, for it

is not desirable to introduce new food into the stomach, until the

gastric digestion of the preceding meal has been completed, and until

the stomach has had time to rest, and is in condition to receive fresh

material. The stomach, like other organs, does its work best at regular

periods.[25]

Eating out of mealtimes should be strictly avoided, for it robs the

stomach of its needed rest. Food eaten when the body and mind are

wearied is not well digested. Rest, even for a few minutes, should be

taken before eating a full meal. It is well to lie down, or sit quietly

and read, fifteen minutes before eating, and directly afterwards, if

possible.

Severe exercise and hard study just after a full meal, are very apt to

delay or actually arrest digestion, for after eating heartily, the

vital forces of the body are called upon to help the stomach digest its

food. If our bodily energies are compelled, in addition to this, to

help the muscles or brain, digestion is retarded, and a feeling of

dullness and heaviness follows. Fermentative changes, instead of the

normal digestive changes, are apt to take place in the food.

167. Practical Points about Eating. We should not eat for at least two

or three hours before going to bed. When we are asleep, the vital

forces are at a low ebb, the process of digestion is for the time

nearly suspended, and the retention of incompletely digested food in

the stomach may cause bad dreams and troubled sleep. But in many cases

of sleeplessness, a trifle of some simple food, especially if the

stomach seems to feel exhausted, often appears to promote sleep and

rest.

Note. The table below shows the results of many experiments to

illustrate the time taken for the gastric digestion of a number of the

more common solid foods. There are a good many factors of which the

table takes no account, such as the interval since the last meal, state

of the appetite, amount of work and exercise, method of cooking, and

especially the quantity of food.

Table Showing the Digestibility of the More Common Solid Foods.

Food How Cooked Time in Stomach, Hours

Apples, sweet and mellow Raw 1½

Apples, sour and hard ” 2½

Apple Dumpling Boiled 3

Bass, striped, fresh Broiled 3

Beans, pod Boiled 2½

Beef, with salt only ” 2¾

” fresh, lean Raw 3

” ” ” Fried 4

” ” ” Roasted 3½

” old, hard, salted Boiled 4¼

Beefsteak Broiled 3

Beets Boiled 3¾

Bread, corn Baked 3¼

” wheat, fresh ” 3½

Butter Melted 3½

Cabbage, with vinegar Raw 2

” ” ” Boiled 4½

” heads Raw 2½

Carrots Boiled 3¼

Cheese, old, strong Raw 3½

Chicken, full-grown Fricassee 2¾

” soup Boiled 3

Codfish, cured, dried ” 2

Corncake Baked 2¾

Custard ” 2¾

Duck, domestic Roasted 4

” wild ” 4½

Eggs, fresh, whipped Raw 1½

” ” 2

” soft-boiled Boiled 3

” hard-boiled ” 3½

” Fried 3½

Fowl, domestic Boiled 4

” ” Roasted 4

Gelatin Boiled 2½

Goose Roasted 2½

Green corn and beans Boiled 3¾

Hash, meat and vegetables Warmed 2½

Lamb Broiled 2½

Liver ” 2

Milk Boiled 2

” Raw 2¼

Mutton, fresh Broiled 3

” ” Boiled 3

” ” Roasted 3¼

Oysters, fresh Raw 2½

” ” Roasted 3¼

” ” Stewed 3½

Parsnips Boiled 2½

Pig Roasted 2½

Pig’s feet, soused Boiled 1

Pork, recently salted ” 4½

” Fried 4¼

” Raw 3

” steaks Fried 3¼

” Stewed 3

” fat or lean Roasted 5¼

Potatoes Baked 2½

” Boiled 3½

” Roasted 2½

Rice Boiled 1

Sago ” 1¾

Salmon, salted ” 4

Soup, barley ” 1½

” beans ” 3

” beef, vegetables, bread ” 4

” marrow bone ” 4½

” mutton ” 3½

Sponge Cake Baked 2½

Suet, beef, fresh Boiled 5⅓

” mutton ” 4½

Tapioca ” 2

Tripe, soused ” 1

Trout, salmon, fresh ” 1½

” ” ” Fried 1½

Turkey, wild Roasted 2¼

” domestic Boiled 2¼

” ” Roasted 2½

Turnips Boiled 3½

Veal Roasted 4

” Fried 4½

Venison, steaks Broiled 1½

The state of mind has much to do with digestion. Sudden fear or joy, or

unexpected news, may destroy the appetite at once. Let a hungry person

be anxiously awaiting a hearty meal, when suddenly a disastrous

telegram is brought him; all appetite instantly disappears, and the

tempting food is refused. Hence we should laugh and talk at our meals,

and drive away anxious thoughts and unpleasant topics of discussion.

The proper chewing of the food is an important element in digestion.

Hence, eat slowly, and do not “bolt” large fragments of food. If

imperfectly chewed, it is not readily acted upon by the gastric juice,

and often undergoes fermentative changes which result in sour stomach,

gastric pain, and other digestive disturbance.

If we take too much drink with our meals, the flow of the saliva is

checked, and digestion is hindered. It is not desireable to dilute the

gastric juice, nor to chill the stomach with large amount of cold

liquid.

Do not take food and drink too hot or too cold. If they are taken too

cold, the stomach is chilled, and digestion delayed. If we drink freely

of ice-water, it may require half an hour or more for the stomach to

regain its natural heat.

It is a poor plan to stimulate a flagging appetite with highly spiced

food and bitter drinks. An undue amount of pepper, mustard,

horseradish, pickles, and highly seasoned meat-sauces may stimulate

digestion for the time, but they soon impair it.

Note. The process of gastric digestion was studied many years ago by

Dr. Beaumont and others, in the remarkable case of Alexis St. Martin, a

French-Canadian, who met with a gun-shot wound which left a permanent

opening into his stomach, guarded by a little valve of mucous membrane.

Through this opening the lining of the stomach could be seen, the

temperature ascertained, and numerous experiments made as to the

digestibility of various kinds of food.

It was by these careful and convincing experiments that the

foundation of our exact knowledge of the composition and action of

gastric juice was laid. The modest book in which Dr. Beaumont

published his results is still counted among the classics of

physiology. The production of artificial fistulæ in animals, a

method that has since proved so fruitful, was first suggested by

his work.

It cannot be too strongly stated that food of a simple character, well

cooked and neatly served, is more productive of healthful living than a

great variety of fancy dishes which unduly stimulate the digestive

organs, and create a craving for food in excess of the bodily needs.

168. The Proper Care of the Teeth. It is our duty not only to take the

very best care of our teeth, but to retain them as long as possible.

Teeth, as we well know, are prone to decay. We may inherit poor and

soft teeth: our mode of living may make bad teeth worse. If an ounce of

prevention is ever worth a pound of cure, it is in keeping the teeth in

good order. Bad teeth and toothless gums mean imperfect chewing of the

food and, hence, impaired digestion. To attain a healthful old age, the

power of vigorous mastication must be preserved.

One of the most frequent causes of decay of the teeth is the retention

of fragments of food between and around them. The warmth and moisture

of the mouth make these matters decompose quickly. The acid thus

generated attacks the enamel of the teeth, causing decay of the

dentine. Decayed teeth are often the cause of an offensive breath and a

foul stomach.

Illustration: Fig. 64.—Lymphatics on the Inside of the Right Hand.

To keep the teeth clean and wholesome, they should be thoroughly

cleansed at bedtime and in the morning with a soft brush and warm

water. Castile soap, and some prepared tooth-powder without grit,

should be used, and the brush should be applied on both sides of the

teeth.

The enamel, once broken through, is never renewed. The tooth decays,

slowly but surely: hence we must guard against certain habits which

injure the enamel, as picking the teeth with pins and needles. We

should never crack nuts, crush hard candy, or bite off stout thread

with the teeth. Stiff tooth-brushes, gritty and cheap tooth-powders,

and hot food and drink, often injure the enamel.

To remove fragments of food which have lodged between adjacent teeth, a

quill or wooden toothpick should be used. Even better than these is the

use of surgeon’s floss, or silk, which when drawn between the teeth,

effectually dislodges retained particles. If the teeth are not

regularly cleansed they become discolored, and a hard coating known as

_tartar_ accumulates on them and tends to loosen them. It is said that

after the age of thirty more teeth are lost from this deposit than from

all other causes combined. In fact decay and tartar are the two great

agents that furnish work for the dentist.[26]

169. Hints about Saving Teeth. We should exercise the greatest care in

saving the teeth. The last resort of all is to lose a tooth by

extraction. The skilled dentist will save almost anything in the shape

of a tooth.

People are often urged and consent to have a number of teeth extracted

which, with but little trouble and expense, might be kept and do good

service for years. The object is to replace the teeth with an

artificial set. Very few plates, either partial or entire, are worn

with real comfort. They should always be removed before going to sleep,

as there is danger of their being swallowed.

The great majority of drugs have no injurious effect upon the teeth.

Some medicines, however, must be used with great care. The acids used

in the tincture of iron have a great affinity for the lime salts of the

teeth. As this form of iron is often used, it is not unusual to see

teeth very badly stained or decayed from the effects of this drug. The

acid used in the liquid preparations of quinine may destroy the teeth

in a comparatively short time. After taking such medicines the mouth

should be thoroughly rinsed with a weak solution of common soda, and

the teeth cleansed.

170. Alcohol and Digestion. The influence of alcoholic drinks upon

digestion is of the utmost importance. Alcohol is not, and cannot be

regarded from a physiological point of view as a true food. The

reception given to it by the stomach proves this very plainly. It is

obviously an unwelcome intruder. It cannot, like proper foods, be

transformed into any element or component of the human body, but passes

on, innutritious and for the most part unappropriated. Taken even into

the mouth, by any person not hardened to its use, its effect is so

pungent and burning as at once to demand its rejection. But if allowed

to pass into the stomach, that organ immediately rebels against its

intrusion, and not unfrequently ejects it with indignant emphasis. The

burning sensation it produces there, is only an appeal for water to

dilute it.

The stomach meanwhile, in response to this fiery invitation, secretes

from its myriad pores its juices and watery fluids, to protect itself

as much as possible from the invading liquid. It does not digest

alcoholic drinks; we might say it does not attempt to, because they are

not material suitable for digestion, and also because no organ can

perform its normal work while smarting under an unnatural irritation.

Even if the stomach does not at once eject the poison, it refuses to

adopt it as food, for it does not pass along with the other food

material, as chyme, into the intestines, but is seized by the

absorbents, borne into the veins, which convey it to the heart, whence

the pulmonary artery conveys it to the lungs, where its presence is

announced in the breath. But wherever alcohol is carried in the

tissues, it is always an irritant, every organ in turn endeavoring to

rid itself of the noxious material.

171. Effect of Alcoholic Liquor upon the Stomach. The methods by which

intoxicating drinks impair and often ruin digestion are various. We

know that a piece of animal food, as beef, if soaked in alcohol for a

few hours, becomes hard and tough, the fibers having been compacted

together because of the abstraction of their moisture by the alcohol,

which has a marvelous affinity for water. In the same way alcohol

hardens and toughens animal food in the stomach, condensing its fibers,

and rendering it indigestible, thus preventing the healthful nutrition

of the body. So, if alcohol be added to the clear, liquid white of an

egg, it is instantly coagulated and transformed into hard albumen. As a

result of this hardening action, animal food in contact with alcoholic

liquids in the stomach remains undigested, and must either be detained

there so long as to become a source of gastric disturbance, or else be

allowed to pass undigested through the pyloric gate, and then may

become a cause of serious intestinal disturbance.[27]

This peculiar property of alcohol, its greedy absorption of water from

objects in contact with it, acts also by absorbing liquids from the

surface of the stomach itself, thus hardening the delicate glands,

impairing their ability to absorb the food-liquids, and so inducing

gastric dyspepsia. This local injury inflicted upon the stomach by all

forms of intoxicants, is serious and protracted. This organ is, with

admirable wisdom, so constructed as to endure a surprising amount of

abuse, but it was plainly not intended to thrive on alcoholic liquids.

The application of fiery drinks to its tender surface produces at first

a marked congestion of its blood-vessels, changing the natural pink

color, as in the mouth, to a bright or deep red.

If the irritation be not repeated, the lining membrane soon recovers

its natural appearance. But if repeated and continued, the congestion

becomes more intense, the red color deeper and darker; the entire

surface is the subject of chronic inflammation, its walls are

thickened, and sometimes ulcerated. In this deplorable state, the organ

is quite unable to perform its normal work of digestion.[28]

172. Alcohol and the Gastric Juice. But still another destructive

influence upon digestion appears in the singular fact that alcohol

diminishes the power of the gastric juice to do its proper work.

Alcohol coagulates the pepsin, which is the dissolving element in this

important gastric fluid. A very simple experiment will prove this.

Obtain a small quantity of gastric juice from the fresh stomach of a

calf or pig, by gently pressing it in a very little water. Pour the

milky juice into a clear glass vessel, add a little alcohol, and a

white deposit will presently settle to the bottom. This deposit

contains the pepsin of the gastric juice, the potent element by which

it does its special work of digestion. The ill effect of alcohol upon

it is one of the prime factors in the long series of evil results from

the use of intoxicants.

173. The Final Results upon Digestion. We have thus explained three

different methods by which alcoholic drinks exercise a terrible power

for harm; they act upon the food so as to render it less digestible;

they injure the stomach so as seriously to impair its power of

digestion; and they deprive the gastric juice of the one principal

ingredient essential to its usefulness.

Alcoholic drinks forced upon the stomach are a foreign substance; the

stomach treats them as such, and refuses to go on with the process of

digestion till it first gets rid of the poison. This irritating

presence and delay weaken the stomach, so that when proper food

follows, the enfeebled organ is ill prepared for its work. After

intoxication, there occurs an obvious reaction of the stomach, and

digestive organs, against the violent and unnatural disturbance. The

appetite is extinguished or depraved, and intense headache racks the

frame, the whole system is prostrated, as from a partial paralysis (all

these results being the voice of Nature’s sharp warning of this great

wrong), and a rest of some days is needed before the system fully

recovers from the injury inflicted.

It is altogether an error to suppose the use of intoxicants is

necessary or even desirable to promote appetite or digestion. In

health, good food and a stomach undisturbed by artificial interference

furnish all the conditions required. More than these is harmful. If it

may sometimes seem as if alcoholic drinks arouse the appetite and

invigorate digestion, we must not shut our eyes to the fact that this

is only a seeming, and that their continued use will inevitably ruin

both. In brief, there is no more sure foe to good appetite and normal

digestion than the habitual use of alcoholic liquors.

174. Effect of Alcoholic Drinks upon the Liver. It is to be noted that

the circulation of the liver is peculiar; that the capillaries of the

hepatic artery unite in the lobule with those of the portal vein, and

thus the blood from both sources is combined; and that the portal vein

brings to the liver the blood from the stomach, the intestines, and the

spleen. From the fact that alcohol absorbed from the stomach enters the

portal vein, and is borne directly to the liver, we would expect to

find this organ suffering the full effects of its presence. And all the

more would this be true, because we have just learned that the liver

acts as a sort of filter to strain from the blood its impurities. So

the liver is especially liable to diseases produced by alcoholics. Post

mortems of those who have died while intoxicated show a larger amount

of alcohol in the liver than in any other organ. Next to the stomach

the liver is an early and late sufferer, and this is especially the

case with hard drinkers, and even more moderate drinkers in hot

climates. Yellow fever occurring in inebriates is always fatal.

The effects produced in the liver are not so much functional as

organic; that is, not merely a disturbed mode of action, but a

destruction of the fabric of the organ itself. From the use of

intoxicants, the liver becomes at first irritated, then inflamed, and

finally seriously diseased. The fine bands, or septa, which serve as

partitions between the hepatic lobules, and so maintain the form and

consistency of the organ, are the special subjects of the inflammation.

Though the liver is at first enlarged, it soon becomes contracted; the

secreting cells are compressed, and are quite unable to perform their

proper work, which indeed is a very important one in the round of the

digestion of food and the purification of the blood. This contraction

of the septa in time gives the whole organ an irregularly puckered

appearance, called from this fact a hob-nail liver or, popularly, gin

liver. The yellowish discoloration, usually from retained or perverted

bile, gives the disease the medical name of cirrhosis.[29] It is

usually accompanied with dropsy in the lower extremities, caused by

obstruction to the return of the circulation from the parts below the

liver. This disease is always fatal.

175. Fatty Degeneration Due to Alcohol. Another form of destructive

disease often occurs. There is an increase of fat globules deposited in

the liver, causing notable enlargement and destroying its function.

This is called fatty degeneration, and is not limited to the liver, but

other organs are likely to be similarly affected. In truth, this

deposition of fat is a most significant occurrence, as it means actual

destruction of the liver tissues,—nothing less than progressive death

of the organ. This condition always leads to a fatal issue. Still other

forms of alcoholic disease of the liver are produced, one being the

excessive formation of sugar, constituting what is known as a form of

diabetes.

176. Effect of Tobacco on Digestion. The noxious influence of tobacco

upon the process of digestion is nearly parallel to the effects of

alcohol, which it resembles in its irritant and narcotic character.

Locally, it stimulates the secretion of saliva to an unnatural extent,

and this excess of secretion diminishes the amount available for normal

digestion.

Tobacco also poisons the saliva furnished for the digestion of food,

and thus at the very outset impairs, in both of these particulars, the

general digestion, and especially the digestion of the starchy portions

of the food. For this reason the amount of food taken, fails to nourish

as it should, and either more food must be taken, or the body becomes

gradually impoverished.

The poisonous _nicotine_, the active element of tobacco, exerts a

destructive influence upon the stomach digestion, enfeebling the vigor

of the muscular walls of that organ. These effects combined produce

dyspepsia, with its weary train of baneful results.

The tobacco tongue never presents the natural, clear, pink color, but

rather a dirty yellow, and is usually heavily coated, showing a

disordered stomach and impaired digestion. Then, too, there is dryness

of the mouth, an unnatural thirst that demands drink. But pure water is

stale and flat to such a mouth: something more emphatic is needed. Thus

comes the unnatural craving for alcoholic liquors, and thus are taken

the first steps on the downward grade.

“There is no doubt that tobacco predisposes to neuralgia, vertigo,

indigestion, and other affections of the nervous, circulatory and

digestive organs.”—W. H. Hammond, the eminent surgeon of New York city

and formerly Surgeon General, U.S.A.

Drs. Seaver of Yale University and Hitchcock of Amherst College,

instructors of physical education in these two colleges, have clearly

demonstrated by personal examination and recorded statistics that the

use of tobacco among college students checks growth in weight, height,

chest-girth, and, most of all, in lung capacity.

Additional Experiments.

Experiment 66. Test a portion of _C_ (Experiment 57) with solution of

iodine; no blue color is obtained, as all the starch has disappeared,

having been converted into a reducing sugar, or maltose.

Experiment 67. Make a thick starch paste; place some in test tubes,

labeled _A_ and _B_. Keep _A_ for comparison, and to _B_ add saliva,

and expose both to about 104° F. _A_ is unaffected, while _B_ soon

becomes fluid—within two minutes—and loses its opalescence; this

liquefaction is a process quite antecedent to the saccharifying process

which follows.

Experiment 68. _To show the action of gastric juice on milk_. Mix two

teaspoonfuls of fresh milk in a test tube with a few drops of neutral

artificial gastric juice;[30] keep at about 100° F. In a short time the

milk curdles, so that the tube can be inverted without the curd falling

out. By and by _whey_ is squeezed out of the clot. The curdling of milk

by the rennet ferment present in the gastric juice, is quite different

from that produced by the “souring of milk,” or by the precipitation of

caseinogen by acids. Here the casein (carrying with it most of the

fats) is precipitated in a neutral fluid.

Experiment 69. To the test tube in the preceding experiment, add two

teaspoonfuls of dilute hydrochloric acid, and keep at 100° F. for two

hours. The pepsin in the presence of the acid digests the casein,

gradually dissolving it, forming a straw-colored fluid containing

peptones. The peptonized milk has a peculiar odor and bitter taste.

Experiment 70. _To show the action of rennet on milk_. Place milk in a

test tube, add a drop or two of commercial rennet, and place the tube

in a water-bath at about 100° F. The milk becomes solid in a few

minutes, forming a _curd_, and by and by the curd of casein contracts,

and presses out a fluid,—the _whey_.

Experiment 71. Repeat the experiment, but previously boil the rennet.

No such result is obtained as in the preceding experiment, because the

rennet ferment is destroyed by heat.

Experiment 72. _To show the effect of the pancreatic ferment (trypsin)

upon albuminous matter_. Half fill three test tubes, _A, B, C_, with

one-per-cent solution of sodium carbonate, and add 5 drops of liquor

pancreaticus, or a few grains of Fairchild’s extract of pancreas, in

each. Boil _B_, and make _C_ acid with dilute hydrochloric acid. Place

in each tube an equal amount of well-washed fibrin, plug the tubes with

absorbent cotton, and place all in a water-bath at about 100° F.

Experiment 73. Examine from time to time the three test tubes in the

preceding experiment. At the end of one, two, or three hours, there is

no change in _B_ and _C_, while in _A_ the fibrin is gradually being

eroded, and finally disappears; but it does not swell up, and the

solution at the same time becomes slightly turbid. After three hours,

still no change is observable in _B_ and _C_.

Experiment 74. Filter _A_, and carefully neutralize the filtrate with

very dilute hydrochloric or acetic acid, equal to a precipitate of

alkali-albumen. Filter off the precipitate, and on testing the

filtrate, peptones are found. The intermediate bodies, the albumoses,

are not nearly so readily obtained from pancreatic as from gastric

digests.

Experiment 75. Filter _B_ and _C_, and carefully neutralize the

filtrates. They give no precipitate. No peptones are found.

Experiment 76. _To show the action of pancreatic juice upon the

albuminous ingredients (casein) of milk_. Into a four-ounce bottle put

two tablespoonfuls of cold water; add one grain of Fairchild’s extract

of pancreas, and as much baking soda as can be taken up on the point of

a penknife. Shake well, and add four tablespoonfuls of cold, fresh

milk. Shake again.

Now set the bottle into a basin of hot water (as hot as one can

bear the hand in), and let it stand for about forty-five minutes.

While the milk is digesting, take a small quantity of milk in a

goblet, and stir in ten drops or more of vinegar. A thick curd of

casein will be seen.

Upon applying the same test to the digested milk, no curd will be

made. This is because the pancreatic ferment (trypsin) has digested

the casein into “peptone,” which does not curdle. This digested

milk is therefore called “peptonized milk.”

Experiment 77. _To show the action of bile_. Obtain from the butcher

some ox bile. Note its bitter taste, peculiar odor, and greenish color.

It is alkaline or neutral to litmus paper. Pour it from one vessel to

another, and note that strings of mucin (from the lining membrane of

the gall bladder) connect one vessel with the other. It is best to

precipitate the mucin by acetic acid before making experiments; and to

dilute the clear liquid with a little distilled water.

Experiment 78. _Test for bile pigments_. Place a few drops of bile on a

white porcelain slab. With a glass rod place a drop or two of strong

nitric acid containing nitrous acid near the drop of bile; bring the

acid and bile into contact. Notice the succession of colors, beginning

with green and passing into blue, red, and yellow.

Experiment 79. _To show the action of bile on fats_. Mix three

teaspoonfuls of bile with one-half a teaspoonful of almond oil, to

which some oleic acid is added. Shake well, and keep the tube in a

water-bath at about 100° F. A very good emulsion is obtained.

Experiment 80. _To show that bile favors filtration and the absorption

of fats_. Place two small funnels of exactly the same size in a filter

stand, and under each a beaker. Into each funnel put a filter paper;

moisten the one with water (_A_) and the other with bile (_B_). Pour

into each an equal volume of almond oil; cover with a slip of glass to

prevent evaporation. Set aside for twelve hours, and note that the oil

passes through _B_, but scarcely any through _A_. The oil filters much

more readily through the one moistened with bile, than through the one

moistened with water.

Experiments with the Fats.

Experiment 81. Use olive oil or lard. Show by experiment that they are

soluble in ether, chloroform and hot water, but insoluble in water

alone.

Experiment 82. Dissolve a few drops of oil or fat in a teaspoonful of

ether. Let a drop of the solution fall on a piece of tissue or rice

paper. Note the greasy stain, which does not disappear with the heat.

Experiment 83. Pour a little cod-liver oil into a test tube; add a few

drops of a dilute solution of sodium carbonate. The whole mass becomes

white, making an emulsion.

Experiment 84. Shake up olive oil with a solution of albumen in a test

tube. Note that an emulsion is formed.

Chapter VII.

The Blood and Its Circulation.

177. The Circulation. All the tissues of the body are traversed by

exceedingly minute tubes called capillaries, which receive the blood

from the arteries, and convey it to the veins. These capillaries form a

great system of networks, the meshes of which are filled with the

elements of the various tissues. That is, the capillaries are closed

vessels, and the tissues lie outside of them, as asbestos packing may

be used to envelop hot-water pipes. The space between the walls of the

capillaries and the cells of the tissues is filled with lymph. As the

blood flows along the capillaries, certain parts of the plasma of the

blood filter through their walls into the lymph, and certain parts of

the lymph filter through the cell walls of the tissues and mingle with

the blood current. The lymph thus acts as a medium of exchange, in

which a transfer of material takes place between the blood in the

capillaries and the lymph around them. A similar exchange of material

is constantly going on between the lymph and the tissues themselves.

This, then, we must remember,—that in every tissue, so long as the

blood flows, and life lasts, this exchange takes place between the

blood within the capillaries and the tissues without.

The stream of blood _to_ the tissues carries to them the material,

including the all-important oxygen, with which they build themselves up

and do their work. The stream _from_ the tissues carries into the blood

the products of certain chemical changes which have taken place in

these tissues. These products may represent simple waste matter to be

cast out or material which may be of use to some other tissue.

In brief, the tissues by the help of the lymph live on the blood. Just

as our bodies, as a whole, live on the things around us, the food and

the air, so do the bodily tissues live on the blood which bathes them

in an unceasing current, and which is their immediate air and food.

178. Physical Properties of Blood. The blood has been called the life

of the body from the fact that upon it depends our bodily existence.

The blood is so essentially the nutrient element that it is called

sometimes very aptly “liquid flesh.” It is a red, warm, heavy, alkaline

fluid, slightly salt in taste, and has a somewhat fetid odor. Its color

varies from bright red in the arteries and when exposed to the air, to

various tints from dark purple to red in the veins. The color of the

blood is due to the coloring constituent of the red corpuscles,

_hæmoglobin_, which is brighter or darker as it contains more or less

oxygen.

Illustration: Fig. 65.—Blood Corpuscles of Various Animals. (Magnified

to the same scale.)

A, from proteus, a kind of newt;

B, salamander;

C, frog;

D, frog after addition of acetic acid, showing the central nucleus;

E, bird;

F, camel;

G, fish;

H, crab or other invertebrate animal

The temperature of the blood varies slightly in different parts of the

circulation. Its average heat near the surface is in health about the

same, _viz_. 98½° F. Blood is alkaline, but outside of the body it soon

becomes neutral, then acid. The chloride of sodium, or common salt,

which the blood contains, gives it a salty taste. In a hemorrhage from

the lungs, the sufferer is quick to notice in the mouth the warm and

saltish taste. The total amount of the blood in the body was formerly

greatly overestimated. It is about 1/13 of the total weight of the

body, and in a person weighing 156 pounds would amount to about 12

pounds.

179. Blood Corpuscles. If we put a drop of blood upon a glass slide,

and place upon it a cover of thin glass, we can flatten it out until

the color almost disappears. If we examine this thin film with a

microscope, we see that the blood is not altogether fluid. We find that

the liquid part, or plasma, is of a light straw color, and has floating

in it a multitude of very minute bodies, called corpuscles. These are

of two kinds, the red and the colorless. The former are much more

numerous, and have been compared somewhat fancifully to countless

myriads of tiny fishes in a swiftly flowing stream.

180. Red Corpuscles. The red corpuscles are circular disks about 1/3200

of an inch in diameter, and double concave in shape. They tend to

adhere in long rolls like piles of coins. They are soft, flexible, and

elastic, readily squeezing through openings and passages narrower than

their own diameter, then at once resuming their own shape.

The red corpuscles are so very small, that rather more than ten

millions of them will lie on a surface one inch square. Their number is

so enormous that, if all the red corpuscles in a healthy person could

be arranged in a continuous line, it is estimated that they would reach

four times around the earth! The principal constituent of these

corpuscles, next to water, and that which gives them color is

_hæmoglobin_, a compound containing iron. As all the tissues are

constantly absorbing oxygen, and giving off carbon dioxid, a very

important office of the red corpuscles is to carry oxygen to all parts

of the body.

181. Colorless Corpuscles. The colorless corpuscles are larger than the

red, their average diameter being about 1/2500 of an inch. While the

red corpuscles are regular in shape, and float about, and tumble freely

over one another, the colorless are of irregular shape, and stick close

to the glass slide on which they are placed. Again, while the red

corpuscles are changed only by some influence from without, as pressure

and the like, the colorless corpuscles spontaneously undergo active and

very curious changes of form, resembling those of the amœba, a very

minute organism found in stagnant water (Fig. 2).

The number of both red and colorless corpuscles varies a great deal

from time to time. For instance, the number of the latter increases

after meals, and quickly diminishes. There is reason to think both

kinds of corpuscles are continually being destroyed, their place being

supplied by new ones. While the action of the colorless corpuscles is

important to the lymph and the chyle, and in the coagulation of the

blood, their real function has not been ascertained.

Illustration: Fig. 66.—Blood Corpuscles of Man.

A, red corpuscles;

B, the same seen edgeways;

C, the same arranged in rows;

D, white corpuscles with nuclei.

Experiment 85. _To show the blood corpuscles_. A moderately powerful

microscope is necessary to examine blood corpuscles. Let a small drop

of blood (easily obtained by pricking the finger with a needle) be

placed upon a clean slip of glass, and covered with thin glass, such as

is ordinarily used for microscopic purposes.

The blood is thus spread out into a film and may be readily examined.

At first the red corpuscles will be seen as pale, disk-like bodies

floating in the clear fluid. Soon they will be observed to stick to

each other by their flattened faces, so as to form rows. The colorless

corpuscles are to be seen among the red ones, but are much less

numerous.

182. The Coagulation of the Blood. Blood when shed from the living body

is as fluid as water. But it soon becomes viscid, and flows less

readily from one vessel to another. Soon the whole mass becomes a

nearly solid jelly called a clot. The vessel containing it even can be

turned upside down, without a drop of blood being spilled. If carefully

shaken out, the mass will form a complete mould of the vessel.

At first the clot includes the whole mass of blood, takes the shape of

the vessel in which it is contained, and is of a uniform color. But in

a short time a pale yellowish fluid begins to ooze out, and to collect

on the surface. The clot gradually shrinks, until at the end of a few

hours it is much firmer, and floats in the yellowish fluid. The white

corpuscles become entangled in the upper portion of clot, giving it a

pale yellow look on the top, known as the _buffy coat_. As the clot is

attached to the sides of the vessel, the shrinkage is more pronounced

toward the center, and thus the surface of the clot is hollowed or

_cupped_, as it is called. This remarkable process is known as

coagulation, or the clotting of blood; and the liquid which separates

from the clot is called serum. The serum is almost entirely free from

corpuscles, these being entangled in the fibrin.

Illustration: Fig. 67.—Diagram of Clot with Buffy Coat.

A, serum;

B, cupped upper surface of clot;

C, white corpuscles in upper layer of clot;

D, lower portion of clot with red corpuscles.

This clotting of the blood is due to the formation in the blood, after

it is withdrawn from the living body, of a substance called fibrin.[31]

It is made up of a network of fine white threads, running in every

direction through the plasma, and is a proteid substance. The

coagulation of the blood may be retarded, and even prevented, by a

temperature below 40° F., or a temperature above 120° F. The addition

of common salt also prevents coagulation. The clotting of the blood may

be hastened by free access to air, by contact with roughened surfaces,

or by keeping it at perfect rest.

This power of coagulation is of the most vital importance. But for

this, a very small cut might cause bleeding sufficient to empty the

blood-vessels, and death would speedily follow. In slight cuts, Nature

plugs up the wound with clots of blood, and thus prevents excessive

bleeding. The unfavorable effects of the want of clotting are

illustrated in some persons in whom bleeding from even the slightest

wounds continues till life is in danger. Such persons are called

“bleeders,” and surgeons hesitate to perform on them any operation,

however trivial, even the extraction of a tooth being often followed by

an alarming loss of blood.

Experiment 86. A few drops of fresh blood may be easily obtained to

illustrate important points in the physiology of blood, by tying a

string tight around the finger, and piercing it with a clean needle.

The blood runs freely, is red and opaque. Put two or three drops of

fresh blood on a sheet of white paper, and observe that it looks

yellowish.

Experiment 87. Put two or three drops of fresh blood on a white

individual butter plate inverted in a saucer of water. Cover it with an

inverted goblet. Take off the cover in five minutes, and the drop has

set into a jelly-like mass. Take it off in half an hour, and a little

clot will be seen in the watery serum.

Experiment 88. _To show the blood-clot._ Carry to the slaughter house a

clean, six or eight ounce, wide-mouthed bottle. Fill it with fresh

blood. Carry it home with great care, and let it stand over night. The

next day the clot will be seen floating in the nearly colorless serum.

Experiment 89. Obtain a pint of fresh blood; put it into a bowl, and

whip it briskly for five minutes, with a bunch of dry twigs. Fine white

threads of fibrin collect on the twigs, the blood remaining fluid. This

is “whipped” or defibrinated blood, which has lost the power of

coagulating spontaneously.

183. General Plan of Circulation. All the tissues of the body depend

upon the blood for their nourishment. It is evident then that this

vital fluid must be continually renewed, else it would speedily lose

all of its life-giving material. Some provision, then, is necessary not

only to have the blood renewed in quantity and quality, but also to

enable it to carry away impurities.

So we must have an apparatus of circulation. We need first a central

pump from which branch off large pipes, which divide into smaller and

smaller branches until they reach the remotest tissues. Through these

pipes the blood must be pumped and distributed to the whole body. Then

we must have a set of return pipes by which the blood, after it has

carried nourishment to the tissues, and received waste matters from

them, shall be brought back to the central pumping station, to be used

again. We must have also some apparatus to purify the blood from the

waste matter it has collected.

Illustration: Fig. 68.—Anterior View of the Heart.

A, superior vena cava;

B, right auricle;

C, right ventricle;

D, left ventricle;

E, left auricle;

F, pulmonary vein;

H, pulmonary artery;

K, aorta;

L, right subclavian artery;

M, right common carotid artery;

N, left common carotid artery.

This central pump is the heart. The pipes leading from it and gradually

growing smaller and smaller are the arteries. The very minute vessels

into which they are at last subdivided are capillaries. The pipes which

convey the blood back to the heart are the veins. Thus, the arteries

end in the tissues in fine, hair-like vessels, the capillaries; and the

veins begin in the tissues in exceedingly small tubes,—the capillaries.

Of course, there can be no break in the continuity between the arteries

and the vein. The apparatus of circulation is thus formed by the heart,

the arteries, the capillaries, and the veins.

184. The Heart. The heart is a pear-shaped, muscular organ roughly

estimated as about the size of the persons closed fist. It lies in the

chest behind the breastbone, and is, lodged between the lobes of the

lungs, which partly cover it. In shape the heart resembles a cone, the

base of which is directed upwards, a little backwards, and to the right

side, while the apex is pointed downwards, forwards, and to the left

side. During life, the apex of the heart beats against the chest wall

in the space between the fifth and sixth ribs, and about an inch and a

half to the left of the middle line of the body. The beating of the

heart can be readily felt, heard, and often seen moving the chest wall

as it strikes against it.

Illustration: Fig. 69.—Diagram illustrating the Structure of a Serous

Membrane.

A, the viscus, or organ, enveloped by serous membrane;

B, layer of membrane lining cavity;

C, membrane reflected to envelop viscus;

D, outer layer of viscus, with blood-vessels at

E communicating with the general circulation.

The heart does not hang free in the chest, but is suspended and kept in

position to some extent by the great vessels connected with it. It is

enclosed in a bell-shaped covering called the pericardium. This is

really double, with two layers, one over another. The inner or serous

layer covers the external surface of the heart, and is reflected back

upon itself in order to form, like all membranes of this kind, a sac

without an opening.[32] The heart is thus covered by the pericardial

sac, but is not contained inside its cavity. The space between the two

membranes is filled with serous fluid. This fluid permits the heart and

the pericardium to glide upon one another with the least possible

amount of friction.[33]

The heart is a hollow organ, but the cavity is divided into two parts

by a muscular partition forming a left and a right side, between which

there is no communication. These two cavities are each divided by a

horizontal partition into an upper and a lower chamber. These

partitions, however, include a set of valves which open like folding

doors between the two rooms. If these doors are closed there are two

separate rooms, but if open there is practically only one room. The

heart thus has four chambers, two on each side. The two upper chambers

are called auricles from their supposed resemblance to the ear. The two

lower chambers are called ventricles, and their walls form the chief

portion of the muscular substance of the organ. There are, therefore,

the right and left auricles, with their thin, soft walls, and the right

and left ventricles, with their thick and strong walls.

185. The Valves of the Heart. The heart is a valvular pump, which works

on mechanical principles, the motive power being supplied by the

contraction of its muscular fibers. Regarding the heart as a pump, its

valves assume great importance. They consist of thin, but strong,

triangular folds of tough membrane which hang down from the edges of

the passages into the ventricles. They may be compared to swinging

curtains which, by opening only one way, allow the blood to flow from

the auricles to the ventricles, but by instantly folding back prevent

its return.

Illustration: Fig. 70.—Lateral Section of the Right Chest. (Showing the

relative position of the heart and its great vessels, the œsophagus and

trachea.)

A, inferior constrictor muscle (aids in conveying food down the

œsophagus);

B, œsophagus;

C, section of the right bronchus;

D, two right pulmonary veins;

E, great azygos vein crossing œsophagus and right bronchus to empty

into the superior vena cava;

F, thoracic duct;

H, thoracic aorta;

K, lower portion of œsophagus passing through the diaphragm;

L, diaphragm as it appears in sectional view, enveloping the heart;

M, inferior vena cava passing through diaphragm and emptying into

auricle;

N, right auricle;

O, section of right branch of the pulmonary artery;

P, aorta;

R, superior vena cava;

S, trachea.

The valve on the right side is called the tricuspid, because it

consists of three little folds which fall over the opening and close

it, being kept from falling too far by a number of slender threads

called chordæ tendinæ. The valve on the left side, called the mitral,

from its fancied resemblance to a bishop’s mitre, consists of two folds

which close together as do those of the tricuspid valve.

The slender cords which regulate the valves are only just long enough

to allow the folds to close together, and no force of the blood pushing

against the valves can send them farther back, as the cords will not

stretch The harder the blood in the ventricles pushes back against the

valves, the tighter the cords become and the closer the folds are

brought together, until the way is completely closed.

From the right ventricle a large vessel called the pulmonary artery

passes to the lungs, and from the left ventricle a large vessel called

the aorta arches out to the general circulation of the body. The

openings from the ventricles into these vessels are guarded by the

semilunar valves. Each valve has three folds, each half-moon-shaped,

hence the name semilunar. These valves, when shut, prevent any backward

flow of the blood on the right side between the pulmonary artery and

the right ventricle, and on the left side between the aorta and the

left ventricle.

Illustration: Fig. 71.—Right Cavities of the Heart.

A, aorta;

B, superior vena cava;

C, C, right pulmonary veins;

D, inferior vena cava;

E, section of coronary vein;

F, right ventricular cavity;

H, posterior curtain of the tricuspid valve;

K, right auricular cavity;

M, fossa ovalis, oval depression, partition between the auricles

formed after birth.

186. General Plan of the Blood-vessels Connected with the Heart. There

are numerous blood-vessels connected with the heart, the relative

position and the use of which must be understood. The two largest veins

in the body, the superior vena cava and the inferior vena cava, open

into the right auricle. These two veins bring venous blood from all

parts of the body, and pour it into the right auricle, whence it passes

into the right ventricle.

From the right ventricle arises one large vessel, the pulmonary artery,

which soon divides into two branches of nearly equal size, one for the

right lung, the other for the left. Each branch, having reached its

lung, divides and subdivides again and again, until it ends in

hair-like capillaries, which form a very fine network in every part of

the lung. Thus the blood is pumped from the right ventricle into the

pulmonary artery and distributed throughout the two lungs (Figs. 86 and

88).

We will now turn to the left side of the heart, and notice the general

arrangement of its great vessels. Four veins, called the pulmonary

veins, open into the left auricle, two from each lung. These veins

start from very minute vessels the continuation of the capillaries of

the pulmonary artery. They form larger and larger vessels until they

become two large veins in each lung, and pour their contents into the

left auricle. Thus the pulmonary artery carries venous blood from the

right ventricle _to_ the lungs, as the pulmonary veins carry arterial

blood _from_ the lungs to the left auricle.

From the left ventricle springs the largest arterial trunk in the body,

over one-half of an inch in diameter, called the aorta. From the aorta

other arteries branch off to carry the blood to all parts of the body,

only to be again brought back by the veins to the right side, through

the cavities of the ventricles. We shall learn in Chapter VIII. that

the main object of pumping the blood into the lungs is to have it

purified from certain waste matters which it has taken up in its course

through the body, before it is again sent on its journey from the left

ventricle.

187. The Arteries. The blood-vessels are flexible tubes through which

the blood is borne through the body. There are three kinds,—the

arteries, the veins, and the capillaries, and these differ from one

another in various ways.

The arteries are the highly elastic and extensible tubes which carry

the pure, fresh blood outwards from the heart to all parts of the body.

They may all be regarded as branches of the aorta. After the aorta

leaves the left ventricle it rises towards the neck, but soon turns

downwards, making a curve known as the arch of the aorta.

From the arch are given off the arteries which supply the head and arms

with blood. These are the two carotid arteries, which run up on each

side of the neck to the head, and the two subclavian arteries, which

pass beneath the collar bone to the arms. This great arterial trunk now

passes down in front of the spine to the pelvis, where it divides into

two main branches, which supply the pelvis and the lower limbs.

The descending aorta, while passing downwards, gives off arteries to

the different tissues and organs. Of these branches the chief are the

cœliac artery, which subdivides into three great branches,—one each to

supply the stomach, the liver, and the spleen; then the renal arteries,

one to each kidney; and next two others, the mesenteric arteries, to

the intestines. The aorta at last divides into two main branches, the

common iliac arteries, which, by their subdivisions, furnish the

arterial vessels for the pelvis and the lower limbs.

Illustration: Fig. 72.—Left Cavities of the Heart.

A, B, right pulmonary veins;

with S, openings of the veins;

E, D, C, aortic valves;

R, aorta;

P, pulmonary artery;

O, pulmonic valves;

H, mitral valve;

K, columnæ carnoeæ;

M, right ventricular cavity;

N, interventricular septum.

The flow of blood in the arteries is caused by the muscular force of

the heart, aided by the elastic tissues and muscular fibers of the

arterial walls, and to a certain extent by the muscles themselves. Most

of the great arterial trunks lie deep in the fleshy parts of the body;

but their branches are so numerous and become so minute that, with a

few exceptions, they penetrate all the tissues of the body,—so much so,

that the point of the finest needle cannot be thrust into the flesh

anywhere without wounding one or more little arteries and thus drawing

blood.

188. The Veins. The veins are the blood-vessels which carry the impure

blood from the various tissues of the body to the heart. They begin in

the minute capillaries at the extremities of the four limbs, and

everywhere throughout the body, and passing onwards toward the heart,

receive constantly fresh accessions on the way from myriad other veins

bringing blood from other wayside capillaries, till the central veins

gradually unite into larger and larger vessels until at length they

form the two great vessels which open into the right auricle of the

heart.

These two great venous trunks are the inferior vena cava, bringing the

blood from the trunk and the lower limbs, and the superior vena cava,

bringing the blood from the head and the upper limbs. These two large

trunks meet as they enter the right auricle. The four pulmonary veins,

as we have learned, carry the arterial blood from the lungs to the left

auricle.

Illustration: Fig. 73.

A, part of a vein laid open, with two pairs of valves;

B, longitudinal section of a vein, showing the valves closed.

A large vein generally accompanies its corresponding artery, but most

veins lie near the surface of the body, just beneath the skin. They may

be easily seen under the skin of the hand and forearm, especially in

aged persons. If the arm of a young person is allowed to hang down a

few moments, and then tightly bandaged above the elbow to retard the

return of the blood, the veins become large and prominent.

The walls of the larger veins, unlike arteries, contain but little of

either elastic or muscular tissue; hence they are thin, and when empty

collapse. The inner surfaces of many of the veins are supplied with

pouch-like folds, or pockets, which act as valves to impede the

backward flow of the blood, while they do not obstruct blood flowing

forward toward the heart. These valves can be shown by letting the

forearm hang down, and sliding the finger upwards over the veins (Fig.

73).

The veins have no force-pump, like the arteries, to propel their

contents towards their destination. The onward flow of the blood in

them is due to various causes, the chief being the pressure behind of

the blood pumped into the capillaries. Then as the pocket-like valves

prevent the backward flow of the blood, the pressure of the various

muscles of the body urges along the blood, and thus promotes the onward

flow.

The forces which drive the blood through the arteries are sufficient to

carry the blood on through the capillaries. It is calculated that the

onward flow in the capillaries is about 1/50 to 1/33 of an inch in a

second, while in the arteries the blood current flows about 16 inches

in a second, and in the great veins about 4 inches every second.

Illustration: Fig. 74.—The Structure of Capillaries.

Capillaries of various sizes, showing cells with nuclei

189. The Capillaries. The capillaries are the minute, hair-like tubes,

with very thin walls, which form the connection between the ending of

the finest arteries and the beginning of the smallest veins. They are

distributed through every tissue of the body, except the epidermis and

its products, the epithelium, the cartilages, and the substance of the

teeth. In fact, the capillaries form a network of the tiniest

blood-vessels, so minute as to be quite invisible, at least one-fourth

smaller than the finest line visible to the naked eye.

The capillaries serve as a medium to transmit the blood from the

arteries to the veins; and it is through them that the blood brings

nourishment to the surrounding tissues. In brief, we may regard the

whole body as consisting of countless groups of little islands

surrounded by ever-flowing streams of blood. The walls of the

capillaries are of the most delicate structure, consisting of a single

layer of cells loosely connected. Thus there is allowed the most free

interchange between the blood and the tissues, through the medium of

the lymph.

The number of the capillaries is inconceivable. Those in the lungs

alone, placed in a continuous line, would reach thousands of miles. The

thin walls of the capillaries are admirably adapted for the important

interchanges that take place between the blood and the tissues.

190. The Circulation of the Blood. It is now well to study the

circulation as a whole, tracing the course of the blood from a certain

point until it returns to the same point. We may conveniently begin

with the portion of blood contained at any moment in the right auricle.

The superior and inferior venæ cavæ are busily filling the auricle with

dark, impure blood. When it is full, it contracts. The passage leading

to the right ventricle lies open, and through it the blood pours till

the ventricle is full. Instantly this begins, in its turn, to contract.

The tricuspid valve at once closes, and blocks the way backward. The

blood is now forced through the open semilunar valves into the

pulmonary artery.

The pulmonary artery, bringing venous blood, by its alternate expansion

and recoil, draws the blood along until it reaches the pulmonary

capillaries. These tiny tubes surround the air cells of the lungs, and

here an exchange takes place. The impure, venous blood here gives up

its _débris_ in the shape of carbon dioxid and water, and in return

takes up a large amount of oxygen. Thus the blood brought to the lungs

by the pulmonary arteries leaves the lungs entirely different in

character and appearance. This part of the circulation is often called

the lesser or pulmonic circulation.

The four pulmonary veins bring back bright, scarlet blood, and pour it

into the left auricle of the heart, whence it passes through the mitral

valve into the left ventricle. As soon as the left ventricle is full,

it contracts. The mitral valve instantly closes and blocks the passage

backward into the auricle; the blood, having no other way open, is

forced through the semilunar valves into the aorta. Now red in color

from its fresh oxygen, and laden with nutritive materials, it is

distributed by the arteries to the various tissues of the body. Here it

gives up its oxygen, and certain nutritive materials to build up the

tissues, and receives certain products of waste, and, changed to a

purple color, passes from the capillaries into the veins.

Illustration: Fig. 75.—Diagram illustrating the Circulation.

1, right auricle;

2, left auricle;

3, right ventricle;

4, left ventricle;

5, vena cava superior;

6, vena cava inferior;

7, pulmonary arteries;

8, lungs;

9, pulmonary veins;

10, aorta;

11, alimentary canal;

12, liver;

13, hepatic artery;

14, portal vein;

15, hepatic vein.

All the veins of the body, except those from the lungs and the heart

itself, unite into two large veins, as already described, which pour

their contents into the right auricle of the heart, and thus the grand

round of circulation is continually maintained. This is called the

systemic circulation. The whole circuit of the blood is thus divided

into two portions, very distinct from each other.

191. The Portal Circulation. A certain part of the systemic or greater

circulation is often called the portal circulation, which consists of

the flow of the blood from the abdominal viscera through the portal

vein and liver to the hepatic vein. The blood brought to the

capillaries of the stomach, intestines, spleen, and pancreas is

gathered into veins which unite into a single trunk called the portal

vein. The blood, thus laden with certain products of digestion, is

carried to the liver by the portal vein, mingling with that supplied to

the capillaries of the same organ by the hepatic artery. From these

capillaries the blood is carried by small veins which unite into a

large trunk, the hepatic vein, which opens into the inferior vena cava.

The portal circulation is thus not an independent system, but forms a

kind of loop on the systemic circulation.

The lymph-current is in a sense a slow and stagnant side stream of the

blood circulation; for substances are constantly passing from the

blood-vessels into the lymph spaces, and returning, although after a

comparatively long interval, into the blood by the great lymphatic

trunks.

Experiment 90. _To illustrate the action of the heart, and how it pumps

the blood in only one direction_. Take a Davidson or Household rubber

syringe. Sink the suction end into water, and press the bulb. As you

let the bulb expand, it fills with water; as you press it again, a

valve prevents the water from flowing back, and it is driven out in a

jet along the other pipe. The suction pipe represents the veins; the

bulb, the heart; and the tube end, out of which the water flows, the

arteries.

Note. The heart is not nourished by the blood which passes through it.

The muscular substance of the heart itself is supplied with nourishment

by two little arteries called the _coronary arteries_, which start from

the aorta just above two of the semilunar valves. The blood is returned

to the right auricle (not to either of the venæ cavæ) by the _coronary

vein_.

The longest route a portion of blood may take from the moment it

leaves the left ventricle to the moment it returns to it, is

through the portal circulation. The shortest possible route is

through the substance of the heart itself. The mean time which the

blood requires to make a complete circuit is about 23 seconds.

192. The Rhythmic Action of the Heart. To maintain a steady flow of

blood throughout the body the action of the heart must be regular and

methodical. The heart does not contract as a whole. The two auricles

contract at the same time, and this is followed at once by the

contraction of the two ventricles. While the ventricles are

contracting, the auricles begin to relax, and after the ventricles

contract they also relax. Now comes a pause, or rest, after which the

auricles and ventricles contract again in the same order as before, and

their contractions are followed by the same pause as before. These

contractions and relaxations of the various parts of the heart follow

one another so regularly that the result is called the rhythmic action

of the heart.

The average number of beats of the heart, under normal conditions, is

from 65 to 75 per minute. Now the time occupied from the instant the

auricles begin to contract until after the contraction of the

ventricles and the pause, is less than a second. Of this time one-fifth

is occupied by the contraction of the auricles, two-fifths by the

contraction of the ventricles, and the time during which the whole

heart is at rest is two-fifths of the period.

193. Impulse and Sounds of the Heart. The rhythmic action of the heart

is attended with various occurrences worthy of note. If the hand be

laid flat over the chest wall on the left, between the fifth and sixth

ribs, the heart will be felt beating. This movement is known as the

beat or impulse of the heart, and can be both seen and felt on the left

side. The heart-beat is unusually strong during active bodily exertion,

and under mental excitement.

The impulse of the heart is due to the striking of the lower, tense

part of the ventricles—the apex of the heart—against the chest wall at

the moment of their vigorous contraction. It is important for the

physician to know the exact place where the heart-beat should be felt,

for the heart may be displaced by disease, and its impulse would

indicate its new position.

Sounds also accompany the heart’s action. If the ear be applied over

the region of the heart, two distinct sounds will be heard following

one another with perfect regularity. Their character may be tolerably

imitated by pronouncing the syllables _lubb_, _dŭp_. One sound is heard

immediately after the other, then there is a pause, then come the two

sounds again. The first is a dull, muffled sound, known as the “first

sound,” followed at once by a short and sharper sound, known as the

“second sound” of the heart.

The precise cause of the first sound is still doubtful, but it is made

at the moment the ventricles contract. The second sound is, without

doubt, caused by the sudden closure of the semilunar valves of the

pulmonary artery and the aorta, at the moment when the contraction of

the ventricles is completed.

Illustration: Fig. 76.—Muscular Fibers of the Ventricles.

A, superficial fibers common to both ventricles;

B, fibers of the left ventricle;

C, deep fibers passing upwards toward the base of the heart;

D, fibers penetrating the left ventricle

The sounds of the heart are modified or masked by blowing “murmurs”

when the cardiac orifices or valves are roughened, dilated, or

otherwise affected as the result of disease. Hence these new sounds may

often afford indications of the greatest importance to physicians in

the diagnosis of heart-disease.

194. The Nervous Control of the Heart. The regular, rhythmic movement

of the heart is maintained by the action of certain nerves. In various

places in the substance of the heart are masses of nerve matter, called

ganglia. From these ganglia there proceed, at regular intervals,

discharges of nerve energy, some of which excite movement, while others

seem to restrain it. The heart would quickly become exhausted if the

exciting ganglia had it all their own way, while it would stand still

if the restraining ganglia had full sway. The influence of one,

however, modifies the other, and the result is a moderate and regular

activity of the heart.

The heart is also subject to other nerve influences, but from outside

of itself. Two nerves are connected with the heart, the pneumogastric

and the sympathetic (secs. 271 and 265). The former appears to be

connected with the restraining ganglia; the latter with the exciting

ganglia. Thus, if a person were the subject of some emotion which

caused fainting, the explanation would be that the impression had been

conveyed to the brain, and from the brain to the heart by the

pneumogastric nerves. The result would be that the heart for an instant

ceases to beat. Death would be the result if the nerve influence were

so great as to restrain the movements of the heart for any appreciable

time.

Again, if the person were the subject of some emotion by which the

heart were beating faster than usual, it would mean that there was sent

from the brain to the heart by the sympathetic nerves the impression

which stimulated it to increased activity.

195. The Nervous Control of the Blood-vessels. The tone and caliber of

the blood-vessels are controlled by certain vaso-motor nerves, which

are distributed among the muscular fibers of the walls. These nerves

are governed from a center in the medulla oblongata, a part of the

brain (sec. 270). If the nerves are stimulated more than usual, the

muscular walls contract, and the quantity of the blood flowing through

them and the supply to the part are diminished. Again, if the stimulus

is less than usual, the vessels dilate, and the supply to the part is

increased.

Now the vaso-motor center may be excited to increased activity by

influences reaching it from various parts of the body, or even from the

brain itself. As a result, the nerves are stimulated, and the vessels

contract. Again, the normal influence of the vaso-motor center may be

suspended for a time by what is known as the inhibitory or restraining

effect. The result is that the tone of the blood-vessels becomes

diminished, and their channels widen.

The effect of this power of the nervous system is to give it a certain

control over the circulation in particular parts. Thus, though the

force of the heart and the general average blood-pressure remain the

same, the state of the circulation may be very different in different

parts of the body. The importance of this local control over the

circulation is of the utmost significance. Thus an organ at work needs

to be more richly supplied with blood than when at rest. For example,

when the salivary glands need to secrete saliva, and the stomach to

pour out gastric juice, the arteries that supply these organs are

dilated, and so the parts are flushed with an extra supply of blood,

and thus are aroused to greater activity.

Again, the ordinary supply of blood to a part may be lessened, so that

the organ is reduced to a state of inactivity, as occurs in the case of

the brain during sleep. We have in the act of blushing a visible

example of sudden enlargement of the smaller arteries of the face and

neck, called forth by some mental emotion which acts on the vaso-motor

center and diminishes its activity. The reverse condition occurs in the

act of turning pale. Then the result of the mental emotion is to cause

the vaso-motor nerves to exercise a more powerful control over the

capillaries, thereby closing them, and thus shutting off the flow of

blood.

Experiment 91. Hold up the ear of a white rabbit against the light

while the animal is kept quiet and not alarmed. The red central artery

can be seen coursing along the translucent organ, giving off branches

which by subdivision become too small to be separately visible, and the

whole ear has a pink color and is warm from the abundant blood flowing

through it. Attentive observation will show also that the caliber of

the main artery is not constant; at somewhat irregular periods of a

minute or more it dilates and contracts a little.

Illustration: Fig. 77.—Some of the Principal Organs of the Chest and

Abdomen. (Blood vessels on the left, muscles on the right.)

In brief, all over the body, the nervous system, by its vaso-motor

centers, is always supervising and regulating the distribution of blood

in the body, sending now more and now less to this or that part.

Illustration: Fig. 78.—Capillary Blood-Vessels in the Web of a Frog’s

Foot, as seen with the Microscope.

196. The Pulse. When the finger is placed on any part of the body where

an artery is located near the surface, as, for example, on the radial

artery near the wrist, there is felt an intermittent pressure,

throbbing with every beat of the heart. This movement, frequently

visible to the eye, is the result of the alternate expansion of the

artery by the wave of blood, and the recoil of the arterial walls by

their elasticity. In other words, it is the wave produced by throwing a

mass of blood into the arteries already full. The blood-wave strikes

upon the elastic walls of the arteries, causing an increased

distention, followed at once by contraction. This regular dilatation

and rigidity of the elastic artery answering to the beats of the heart,

is known as the pulse.

The pulse may be easily found at the wrist, the temple, and the inner

side of the ankle. The throb of the two carotid arteries may be plainly

felt by pressing the thumb and finger backwards on each side of the

larynx. The progress of the pulse-wave must not be confused with the

actual current of the blood itself. For instance, the pulse-wave

travels at the rate of about 30 feet a second, and takes about 1/10 of

a second to reach the wrist, while the blood itself is from 3 to 5

seconds in reaching the same place.

The pulse-wave may be compared to the wave produced by a stiff breeze

on the surface of a slowly moving stream, or the jerking throb sent

along a rope when shaken. The rate of the pulse is modified by age,

fatigue, posture, exercise, stimulants, disease, and many other

circumstances. At birth the rate is about 140 times a minute, in early

infancy, 120 or upwards, in the healthy adult between 65 and 75, the

most common number being 72. In the same individual, the pulse is

quicker when standing than when lying down, is quickened by excitement,

is faster in the morning, and is slowest at midnight. In old age the

pulse is faster than in middle life; in children it is quicker than in

adults.

Illustration: Fig. 79.—Circulation in the Capillaries, as seen with the

Microscope.

As the pulse varies much in its rate and character in disease, it is to

the skilled touch of the physician an invaluable help in the diagnosis

of the physical condition of his patient.

Experiment 92. _To find the pulse_. Grasp the wrist of a friend,

pressing with three fingers over the radius. Press three fingers over

the radius in your own wrist, to feel the pulse.

Count by a watch the rate of your pulse per minute, and do the same

with a friend’s pulse. Compare its characters with your own pulse.

Observe how the character and frequency of the pulse are altered by

posture, muscular exercise, a prolonged, sustained, deep

inspiration, prolonged expiration, and other conditions.

197. Effect of Alcoholic Liquors upon the Organs of Circulation.

Alcoholic drinks exercise a destructive influence upon the heart, the

circulation, and the blood itself. These vicious liquids can reach the

heart only indirectly, either from the stomach by the portal vein to

the liver, and thence to the heart, or else by way of the lacteals, and

so to the blood through the thoracic duct. But by either course the

route is direct enough, and speedy enough to accomplish a vast amount

of ruinous work.

The influence of alcohol upon the heart and circulation is produced

mainly through the nervous system. The inhibitory nerves, as we have

seen, hold the heart in check, exercise a restraining control over it,

very much as the reins control an active horse. In health this

inhibitory influence is protective and sustaining. But now comes the

narcotic invasion of alcoholic drinks, which paralyze the inhibitory

nerves, with the others, and at once the uncontrolled heart, like the

unchecked steed, plunges on to violent and often destructive results.

Illustration: Fig. 80.—Two Principal Arteries of the Front of the Leg

(Anterior Tibial and Dorsalis Pedis).

This action, because it is quicker, has been considered also a stronger

action, and the alcohol has therefore been supposed to produce a

stimulating effect. But later researches lead to the conclusion that

the effect of alcoholic liquors is not properly that of a stimulant,

but of a narcotic paralyzant, and that while it indeed quickens, it

also really weakens the heart’s action. This view would seem sustained

by the fact that the more the intoxicants are pushed, the deeper are

the narcotic and paralyzing effects. After having obstructed the

nutritive and reparative functions of the vital fluid for many years,

their effects at last may become fatal.

This relaxing effect involves not only the heart, but also the

capillary system, as is shown in the complexion of the face and the

color of the hands. In moderate drinkers the face is only flushed, but

in drunkards it is purplish. The flush attending the early stages of

drinking is, of course, not the flush of health, but an indication of

disease.[34]

198. Effect upon the Heart. This forced overworking of the heart which

drives it at a reckless rate, cuts short its periods of rest and

inevitably produces serious heart-exhaustion. If repeated and

continued, it involves grave changes of the structure of the heart. The

heart muscle, endeavoring to compensate for the over-exertion, may

become much thickened, making the ventricles smaller, and so fail to do

its duty in properly pumping forward the blood which rushes in from the

auricle. Or the heart wall may by exhaustion become thinner, making the

ventricles much too large, and unable to send on the current. In still

other cases, the heart degenerates with minute particles of fat

deposited in its structures, and thus loses its power to propel the

nutritive fluid. All three of these conditions involve organic disease

of the valves, and all three often produce fatal results.

199. Effect of Alcohol on the Blood-vessels. Alcoholic liquors injure

not only the heart, but often destroy the blood-vessels, chiefly the

larger arteries, as the arch of the aorta or the basilar artery of the

brain. In the walls of these vessels may be gradually deposited a

morbid product, the result of disordered nutrition, sometimes chalky,

sometimes bony, with usually a dangerous dilatation of the tube.

In other cases the vessels are weakened by an unnatural fatty deposit.

Though these disordered conditions differ somewhat, the morbid results

in all are the same. The weakened and stiffened arterial walls lose the

elastic spring of the pulsing current. The blood fails to sweep on with

its accustomed vigor. At last, owing perhaps to the pressure, against

the obstruction of a clot of blood, or perhaps to some unusual strain

of work or passion, the enfeebled vessel bursts, and death speedily

ensues from a form of apoplexy.

Illustration: Fig. 81.—Showing the Carotid Artery and Jugular Vein on

the Right Side, with Some of their Main Branches. (Some branches of the

cervical plexus, and the hypoglossal nerve are also shown.)

Note. “An alcoholic heart loses its contractile and resisting power,

both through morbid changes in its nerve ganglia and in its muscle

fibers. In typhoid fever, muscle changes are evidently the cause of the

heart-enfeeblement; while in diphtheria, disturbances in innervation

cause the heart insufficiency. ‘If the habitual use of alcohol causes

the loss of contractile and resisting power by impairment of both the

nerve ganglia and muscle fibers of the heart, how can it act as a heart

tonic?’”—Dr. Alfred L. Loomis, Professor of Medicine in the Medical

Department of the University of the City of New York.

200. Other Results from the Use of Intoxicants. Other disastrous

consequences follow the use of intoxicants, and these upon the blood.

When any alcohol is present in the circulation, its greed for water

induces the absorption of moisture from the red globules of the blood,

the oxygen-carriers. In consequence they contract and harden, thus

becoming unable to absorb, as theretofore, the oxygen in the lungs.

Then, in turn, the oxidation of the waste matter in the tissues is

prevented; thus the corpuscles cannot convey carbon dioxid from the

capillaries, and this fact means that some portion of refuse material,

not being thus changed and eliminated, must remain in the blood,

rendering it impure and unfit for its proper use in nutrition. Thus,

step by step, the use of alcoholics impairs the functions of the blood

corpuscles, perverts nutrition, and slowly poisons the blood.

Illustration: Fig. 82.—The Right Axillary and Brachial Arteries, with

Some of their Main Branches.

Note. “Destroy or paralyze the inhibitory nerve center, and instantly

its controlling effect on the heart mechanism is lost, and the

accelerating agent, being no longer under its normal restraint, runs

riot. The heart’s action is increased, the pulse is quickened, an

excess of blood is forced into the vessels, and from their becoming

engorged and dilated the face gets flushed, all the usual concomitants

of a general engorgement of the circulation being the result.”—Dr.

George Harley, F.R.S., an eminent English medical author.

“The habitual use of alcohol produces a deleterious influence upon

the whole economy. The digestive powers are weakened, the appetite

is impaired, and the muscular system is enfeebled. The blood is

impoverished, and nutrition is imperfect and disordered, as shown

by the flabbiness of the skin and muscles, emaciation, or an

abnormal accumulation of fat.”—Dr. Austin Flint, Senior, formerly

Professor of the Practice of Medicine in Bellevue Medical College,

and author of many standard medical works.

“The immoderate use of the strong kind of tobacco, which soldiers

affect, is often very injurious to them, especially to very young

soldiers. It renders them nervous and shaky, gives rise to

palpitation, and is a factor in the production of the irritable or

so-called “trotting-heart” and tends to impair the appetite and

digestion.”—London _Lancet_.

“I never smoke because I have seen the most efficient proofs of the

injurious effects of tobacco on the nervous system.”—Dr.

Brown-Sequard, the eminent French physiologist.

“Tobacco, and especially cigarettes, being a depressant upon the

heart, should be positively forbidden.”—Dr. J. M. Keating, on

“Physical Development,” in _Cyclopœdia of the Diseases of

Children_.

201. Effect of Tobacco upon the Heart. While tobacco poisons more or

less almost every organ of the body, it is upon the heart that it works

its most serious wrong. Upon this most important organ its destructive

effect is to depress and paralyze. Especially does this apply to the

young, whose bodies are not yet knit into the vigor that can brave

invasion.

The _nicotine_ of tobacco acts through the nerves that control the

heart’s action. Under its baneful influence the motions of the heart

are irregular, now feeble and fluttering, now thumping with apparently

much force: but both these forms of disturbed action indicate an

abnormal condition. Frequently there is severe pain in the heart, often

dizziness with gasping breath, extreme pallor, and fainting.

The condition of the pulse is a guide to this state of the heart. In

this the physician reads plainly the existence of the “tobacco heart,”

an affection as clearly known among medical men as croup or measles.

There are few conditions more distressing than the constant and

impending suffering attending a tumultuous and fluttering heart. It is

stated that one in every four of tobacco-users is subject, in some

degree, to this disturbance. Test examinations of a large number of

lads who had used cigarettes showed that only a very small percentage

escaped cardiac trouble. Of older tobacco-users there are very few but

have some warning of the hazard they invoke. Generally they suffer more

or less from the tobacco heart, and if the nervous system or the heart

be naturally feeble, they suffer all the more speedily and intensely.

Additional Experiments.

Experiment 93. Touch a few drops of blood fresh from the finger, with a

strip of dry, smooth, neutral litmus paper, highly glazed to prevent

the red corpuscles from penetrating into the test paper. Allow the

blood to remain a short time; then wash it off with a stream of

distilled water, when a blue spot upon a red or violet ground will be

seen, indicating its _alkaline_ reaction, due chiefly to the sodium

phosphate and sodium carbonate.

Experiment 94. Place on a glass slide a thin layer of defibrinated

blood; try to read printed matter through it. This cannot be done.

Experiment 95. _To make blood transparent or laky_. Place in each of

three test tubes two or three teaspoonfuls of defibrinated blood,

obtained from Experiment 89, labeled _A, B_, and _C. A_ is for

comparison. To _B_ add five volumes of water, and warm slightly, noting

the change of color by reflected and transmitted light. By reflected

light it is much darker,—it looks almost black; but by transmitted

light it is transparent. Test this by looking at printed matter as in

Experiment 94.

Experiment 96. To fifteen or twenty drops of defibrinated blood in a

test tube (labeled _D_) add five volumes of a 10-per-cent solution of

common salt. It changes to a very bright, florid, brick-red color.

Compare its color with _A, B_, and _C_. It is opaque.

Experiment 97. Wash away the coloring matter from the twigs (see

Experiment 89) with a stream of water until the fibrin becomes quite

white. It is white, fibrous, and elastic. Stretch some of the fibers to

show their extensibility; on freeing them, they regain their

elasticity.

Experiment 98. Take some of the serum saved from Experiment 88 and note

that it does not coagulate spontaneously. Boil a little in a test tube

over a spirit lamp, and the albumen will coagulate.

Experiment 99. _To illustrate in a general way that blood is really a

mass of red bodies which give the red color to the fluid in which they

float._ Fill a clean white glass bottle two-thirds full of little red

beads, and then fill the bottle full of water. At a short distance the

bottle appears to be rilled with a uniformly red liquid.

Experiment 100. _To show how blood holds a mineral substance in

solution_. Put an egg-shell crushed fine, into a glass of water made

acid by a teaspoonful of muriatic acid. After an hour or so the

egg-shell will disappear, having been dissolved in the acid water. In

like manner the blood holds various minerals in solution.

Experiment 101. _To hear the sounds of the heart_. Locate the heart

exactly. Note its beat. Borrow a stethoscope from some physician.

Listen to the heart-beat of some friend. Note the sounds of your own

heart in the same way.

Experiment 102. _To show how the pulse may be studied_.“The movements

of the artery in the human body as the pulse-wave passes through it may

be shown to consist in a sudden dilatation, followed by a slow

contraction, interrupted by one or more secondary dilatations. This

demonstration may be made by pressing a small piece of looking-glass

about one centimeter square (⅔ of an inch) upon the wrist over the

radial artery, in such a way that with each pulse beat the mirror may

be slightly tilted. If the wrist be now held in such a position that

sunlight will fall upon the mirror, a spot of light will be reflected

on the opposite side of the room, and its motion upon the wall will

show that the expansion of the artery is a sudden movement, while the

subsequent contraction is slow and interrupted.”—Bowditch’s _Hints for

Teachers of Physiology_.

Illustration: Fig. 83.—How the Pulse may be studied by Pressing a

Mirror over the Radial Artery.

Experiment 103. _To illustrate the effect of muscular exercise in

quickening the pulse_. Run up and down stairs several times. Count the

pulse both before and after. Note the effect upon the rate.

Experiment 104. _To show the action of the elastic walls of the

arteries._ Take a long glass or metal tube of small caliber. Fasten one

end to the faucet of a water-pipe (one in a set bowl preferred) by a

very short piece of rubber tube. Turn the water on and off alternately

and rapidly, to imitate the intermittent discharge of the ventricles.

The water will flow from the other end of the rubber pipe in jets, each

jet ceasing the moment the water is shut off.

The experiment will be more successful if the rubber bulb attached

to an ordinary medicine-dropper be removed, and the tapering glass

tube be slipped on to the outer end of the rubber tube attached to

the faucet.

Experiment 105. Substitute a piece of rubber tube for the glass tube,

and repeat the preceding experiment. Now it will be found that a

continuous stream flows from the tube. The pressure of water stretches

the elastic tube, and when the stream is turned off, the rubber recoils

on the water, and the intermittent flow is changed into a continuous

stream.

Experiment 106. _To illustrate some of the phenomena of circulation._

Take a common rubber bulb syringe, of the Davidson, Household, or any

other standard make. Attach a piece of rubber tube about six or eight

feet long to the delivery end of the syringe.

To represent the resistance made by the capillaries to the flow of

blood, slip the large end of a common glass medicine-dropper into

the outer end of the rubber tube. This dropper has one end tapered

to a fine point.

Place the syringe flat, without kinks or bends, on a desk or table.

Press the bulb slowly and regularly. The water is thus pumped into

the tube in an intermittent manner, and yet it is forced out of the

tapering end of the glass tube in a steady flow.

Experiment 107. Take off the tapering glass tube, or, in the place of

one long piece of rubber tube, substitute several pieces of glass

tubing connected together by short pieces of rubber tubes. The obstacle

to the flow has thus been greatly lessened, and the water flows out in

intermittent jets to correspond to the compression of the bulb.

Chapter VIII.

Respiration.

202. Nature and Object of Respiration. The blood, as we have learned,

not only provides material for the growth and activity of all the

tissues of the body, but also serves as a means of removing from them

the products of their activity. These are waste products, which if

allowed to remain, would impair the health of the tissues. Thus the

blood becomes impoverished both by the addition of waste material, and

from the loss of its nutritive matter.

We have shown, in the preceding chapter, how the blood carries to the

tissues the nourishment it has absorbed from the food. We have now to

consider a new source of nourishment to the blood, _viz._, that which

it receives from the oxygen of the air. We are also to learn one of the

methods by which the blood gets rid of poisonous waste matters. In

brief, we are to study the set of processes known as respiration, by

which oxygen is supplied to the various tissues, and by which the

principal waste matters, or chief products of oxidation, are removed.

Now, the tissues are continually feeding on the life-giving oxygen, and

at the same time are continually producing carbon dioxid and other

waste products. In fact, the life of the tissues is dependent upon a

continual succession of oxidations and deoxidations. When the blood

leaves the tissues, it is poorer in oxygen, is burdened with carbon

dioxid, and has had its color changed from bright scarlet to purple

red. This is the change from the arterial to venous conditions which

has been described in the preceding chapter.

Now, as we have seen, the change from venous to arterial blood occurs

in the capillaries of the lungs, the only means of communication

between the pulmonary arteries and the pulmonary veins. The blood in

the pulmonary capillaries is separated from the air only by a delicate

tissue formed of its own wall and the pulmonary membrane. Hence a

gaseous interchange, the essential step in respiration, very readily

takes place between the blood and the air, by which the latter gains

moisture and carbon dioxid, and loses its oxygen. These changes in the

lungs also restore to the dark blood its rosy tint.

The only condition absolutely necessary to the purification of the

blood is an organ having a delicate membrane, on one side of which is a

thin sheet of blood, while the other side is in such contact with the

air that an interchange of gases can readily take place. The demand for

oxygen is, however, so incessant, and the accumulation of carbon dioxid

is so rapid in every tissue of the human body, that an All-Wise Creator

has provided a most perfect but complicated set of machinery to effect

this wonderful purification of the blood.

We are now ready to begin the study of the arrangement and working of

the respiratory apparatus. With its consideration, we complete our view

of the sources of supply to the blood, and begin our study of its

purification.

Illustration: Fig. 84.—The Epiglottis.

203. The Trachea, or Windpipe. If we look into the mouth of a friend,

or into our own with a mirror, we see at the back part an arch which is

the boundary line of the mouth proper. There is just behind this a

similar limit for the back part of the nostrils. The funnel-shaped

cavity beyond, into which both the mouth and the posterior nasal

passages open, is called the pharynx. In its lower part are two

openings; the trachea, or windpipe, in front, and the œsophagus behind.

The trachea is surmounted by a box-like structure of cartilage, about

four and one-half inches long, called the larynx. The upper end of the

larynx opens into the pharynx or throat, and is provided with a lid,—

the epiglottis,—which closes under certain circumstances (secs. 137 and

349). The larynx contains the organ of voice, and is more fully

described in Chapter XII.

The continuation of the larynx is the trachea, a tube about

three-fourths of an inch in diameter, and about four inches long. It

extends downwards along the middle line of the neck, where it may

readily be felt in front, below the Adam’s apple.

Illustration: Fig. 85.—Larynx, Trachea, and the Bronchi. (Front view.)

A, epiglottis;

B, thyroid cartilage;

C, cricoid-thyroid membrane, connecting with the cricoid cartilage

below, all forming the larynx;

D, one of the rings of the trachea.

The walls of the windpipe are strengthened by a series of cartilaginous

rings, each somewhat the shape of a horseshoe or like the letter C,

being incomplete behind, where they come in contact with the œsophagus.

Thus the trachea, while always open for the passage of air, admits of

the distention of the food-passage.

204. The Bronchial Tubes. The lower end of the windpipe is just behind

the upper part of the sternum, and there it divides into two branches,

called bronchi. Each branch enters the lung of its own side, and breaks

up into a great number of smaller branches, called bronchial tubes.

These divide into smaller tubes, which continue subdividing till the

whole lung is penetrated by the branches, the extremities of which are

extremely minute. To all these branches the general name of bronchial

tubes is given. The smallest are only about one-fiftieth of an inch in

diameter.

Illustration: Fig. 86.—Relative Position of the Lungs, Heart, and its

Great Vessels.

A, left ventricle;

B, right ventricle;

C, left auricle;

D, right auricle;

E, superior vena cava;

F, pulmonary artery;

G, aorta;

H, arch of the aorta;

K, innominate artery;

L, right common carotid artery;

M, right subclavian artery;

N, thyroid cartilage forming upper portion of the larynx;

O, trachea.

Now the walls of the windpipe, and of the larger bronchial tubes would

readily collapse, and close the passage for air, but for a wise

precaution. The horseshoe-shaped rings of cartilage in the trachea and

the plates of cartilage in the bronchial tubes keep these passages

open. Again, these air passages have elastic fibers running the length

of the tubes, which allow them to stretch and bend readily with the

movements of the neck.

205. The Cilia of the Air Passages. The inner surfaces of the windpipe

and bronchial tubes are lined with mucous membrane, continuous with

that of the throat, the mouth, and the nostrils, the secretion from

which serves to keep the parts moist.

Delicate, hair-like filaments, not unlike the pile on velvet, called

cilia, spring from the epithelial lining of the air tubes. Their

constant wavy movement is always upwards and outwards, towards the

mouth. Thus any excessive secretion, as of bronchitis or catarrh, is

carried upwards, and finally expelled by coughing. In this way, the

lungs are kept quite free from particles of foreign matter derived from

the air. Otherwise we should suffer, and often be in danger from the

accumulation of mucus and dust in the air passages. Thus these tiny

cilia act as dusters which Nature uses to keep the air tubes free and

clean (Fig. 5).

Illustration: Fig. 87.—Bronchial tube, with its Divisions and

Subdivisions. (Showing groups of air cells at the termination of minute

bronchial tubes.)

206. The Lungs. The lungs, the organs of respiration, are two pinkish

gray structures of a light, spongy appearance, that fill the chest

cavity, except the space taken up by the heart and large vessels.

Between the lungs are situated the large bronchi, the œsophagus, the

heart in its pericardium, and the great blood-vessels. The base of the

lungs rests on the dome-like diaphragm, which separates the chest from

the abdomen. This partly muscular and partly tendinous partition is a

most important factor in breathing.

Each lung is covered, except at one point, with an elastic serous

membrane in a double layer, called the pleura. One layer closely

envelops the lung, at the apex of which it is reflected to the wall of

the chest cavity of its own side, which it lines. The two layers thus

form between them a Closed Sac a serous cavity (see Fig. 69, also note,

p. 176).

Illustration: Fig. 88.—The Lungs with the Trachea, Bronchi, and Larger

Bronchial Tubes exposed. (Posterior view.)

A, division of left bronchus to upper lobe;

B, left branch of the Pulmonary artery;

C, left bronchus;

D, left superior pulmonary vein;

E, left inferior pulmonary vein;

F, left auricle;

K, inferior vena cava;

L, division of right bronchus to lower lobe;

M, right inferior pulmonary vein;

N, right superior pulmonary vein;

O, right branch of the pulmonary artery;

P, division of right bronchus to upper lobe;

R, left ventricle;

S, right ventricle.

In health the two pleural surfaces of the lungs are always in contact,

and they secrete just enough serous fluid to allow the surfaces to

glide smoothly upon each other. Inflammation of this membrane is called

_pleurisy_. In this disease the breathing becomes very painful, as the

secretion of glairy serum is suspended, and the dry and inflamed

surfaces rub harshly upon each other.

The root of the lung, as it is called, is formed by the bronchi, two

pulmonary arteries, and two pulmonary veins. The nerves and lymphatic

vessels of the lung also enter at the root. If we only remember that

all the bronchial tubes, great and small, are hollow, we may compare

the whole system to a short bush or tree growing upside down in the

chest, of which the trachea is the trunk, and the bronchial tubes the

branches of various sizes.

207. Minute Structure of the Lungs. If one of the smallest bronchial

tubes be traced in its tree-like ramifications, it will be found to end

in an irregular funnel-shaped passage wider than itself. Around this

passage are grouped a number of honeycomb-like sacs, the air cells[35]

or alveoli of the lungs. These communicate freely with the passage, and

through it with the bronchial branches, but have no other openings. The

whole arrangement of passages and air cells springing from the end of a

bronchial tube, is called an ultimate lobule. Now each lobule is a very

small miniature of a whole lung, for by the grouping together of these

lobules another set of larger lobules is formed.

Illustration: Fig. 89.

A, diagrammatic representation of the ending of a bronchial tube in

air sacs or alveoli;

B, termination of two bronchial tubes in enlargement beset with air

sacs (_Huxley_);

C, diagrammatic view of an air sac.

a lies within sac and points to epithelium lining wall;

b, partition between two adjacent sacs, in which run capillaries;

c, elastic connective tissue (_Huxley_).

In like manner countless numbers of these lobules, bound together by

connective tissue, are grouped after the same fashion to form by their

aggregation the lobes of the lung. The right lung has three such lobes;

and the left, two. Each lobule has a branch of the pulmonary artery

entering it, and a similar rootlet of the pulmonary vein leaving it. It

also receives lymphatic vessels, and minute twigs of the pulmonary

plexus of nerves.

Illustration: Fig. 90.—Diagram to illustrate the Amounts of Air

contained by the Lungs in Various Phases of Ordinary and of Forced

Respiration.

The walls of the air cells are of extreme thinness, consisting of

delicate elastic and connective tissue, and lined inside by a single

layer of thin epithelial cells. In the connective tissue run capillary

vessels belonging to the pulmonary artery and veins. Now these delicate

vessels running in the connective tissue are surrounded on all sides by

air cells. It is evident, then, that the blood flowing through these

capillaries is separated from the air within the cells only by the thin

walls of the vessels, and the delicate tissues of the air cells.

This arrangement is perfectly adapted for an interchange between the

blood in the capillaries and the air in the air cells. This will be

more fully explained in sec. 214.

208. Capacity of the Lungs. In breathing we alternately take into and

expel from the lungs a certain quantity of air. With each quiet

inspiration about 30 cubic inches of air enter the lungs, and 30 cubic

inches pass out with each expiration. The air thus passing into and out

of the lungs is called tidal air. After an ordinary inspiration, the

lungs contain about 230 cubic inches of air. By taking a deep

inspiration, about 100 cubic inches more can be taken in. This extra

amount is called complemental air.

After an ordinary expiration, about 200 cubic inches are left in the

lungs, but by forced expiration about one-half of this may be driven

out. This is known as supplemental air. The lungs can never be entirely

emptied of air, about 75 to 100 cubic inches always remaining. This is

known as the residual air.

The air that the lungs of an adult man are capable of containing is

thus composed:

Complemental air 100 cubic inches.

Tidal 30 ” ”

Supplemental 100 ” ”

Residual 100 ” ”

Total capacity of lungs 330 ” ”

If, then, a person proceeds, after taking the deepest possible breath, to breath out as much as he can, he expels:

Complemental air 100 cubic inches.

Tidal 30 ” ”

Supplemental 100 ” ”

230

209. The Movements of Breathing. The act of breathing consists of a

series of rhythmical movements, succeeding one another in regular

order. In the first movement, inspiration, the chest rises, and there

is an inrush of fresh air; this is at once followed by expiration, the

falling of the chest walls, and the output of air. A pause now occurs,

and the same breathing movements are repeated.

The entrance and the exit of air into the respiratory passages are

accompanied with peculiar sounds which are readily heard on placing the

ear at the chest wall. These sounds are greatly modified in various

pulmonary diseases, and hence are of great value to the physician in

making a correct diagnosis.

In a healthy adult, the number of respirations should be from 16 to 18

per minute, but they vary with age, that of a newly born child being 44

for the same time. Exercise increases the number, while rest diminishes

it. In standing, the rate is more than when lying at rest. Mental

emotion and excitement quicken the rate. The number is smallest during

sleep. Disease has a notable effect upon the frequency of respirations.

In diseases involving the lungs, bronchial tubes, and the pleura, the

rate may be alarmingly increased, and the pulse is quickened in

proportion.

210. The Mechanism of Breathing. The chest is a chamber with bony

walls, the ribs connecting in front with the breastbone, and behind

with the spine. The spaces between the ribs are occupied by the

intercostal muscles, while large muscles clothe the entire chest. The

diaphragm serves as a movable floor to the chest, which is an air-tight

chamber with movable walls and floor. In this chamber are suspended the

lungs, the air cells of which communicate with the outside through the

bronchial passages, but have no connection with the chest cavity. The

thin space between the lungs and the rib walls, called the pleural

cavity, is in health a vacuum.

Now, when the diaphragm contracts, it descends and thus increases the

depth of the chest cavity. A quantity of air is now drawn into the

lungs and causes them to expand, thus filling up the increased space.

As soon as the diaphragm relaxes, returning to its arched position and

reducing the size of the chest cavity, the air is driven from the

lungs, which then diminish in size. After a short pause, the diaphragm

again contracts, and the same round of operation is constantly

repeated.

The walls of the chest being movable, by the contractions of the

intercostals and other muscles, the ribs are raised and the breastbone

pushed forward. The chest cavity is thus enlarged from side to side and

from behind forwards. Thus, by the simultaneous descent of the

diaphragm and the elevation of the ribs, the cavity of the chest is

increased in three directions,—downwards, side-ways, and from behind

forwards.

It is thus evident that inspiration is due to a series of muscular

contractions. As soon as the contractions cease, the elastic lung

tissue resumes its original position, just as an extended rubber band

recovers itself. As a result, the original size of the chest cavity is

restored, and the inhaled air is driven from the lungs. Expiration may

then be regarded as the result of an elastic recoil, and not of active

muscular contractions.

Illustration: Fig. 91.—Diagrammatic Section of the Trunk. (Showing the

expansion of the chest and the movement of the ribs by action of the

lungs.) [The dotted lines indicate the position during inspiration.]

211. Varieties of Breathing. This is the mechanism of quiet, normal

respiration. When the respiration is difficult, additional forces are

brought into play. Thus when the windpipe and bronchial tubes are

obstructed, as in croup, asthma, or consumption, many additional

muscles are made use of to help the lungs to expand. The position which

asthmatics often assume, with arms raised to grasp something for

support, is from the need of the sufferer to get a fixed point from

which the muscles of the arm and chest may act forcibly in raising the

ribs, and thus securing more comfortable breathing.

The visible movements of breathing vary according to circumstances. In

infants the action of the diaphragm is marked, and the movements of the

abdomen are especially obvious. This is called abdominal breathing. In

women the action of the ribs as they rise and fall, is emphasized more

than in men, and this we call costal breathing. In young persons and in

men, the respiration not usually being impeded by tight clothing, the

breathing is normal, being deep and abdominal.

Disease has a marked effect upon the mode of breathing. Thus, when

children suffer from some serious chest disease, the increased

movements of the abdominal walls seem distressing. So in fracture of

the ribs, the surgeon envelops the overlying part of the chest with

long strips of firm adhesive plaster to restrain the motions of chest

respiration, that they may not disturb the jagged ends of the broken

bones. Again, in painful diseases of the abdomen, the sufferer

instinctively suspends the abdominal action and relies upon the chest

breathing. These deviations from the natural movements of respiration

are useful to the physician in ascertaining the seat of disease.

212. The Nervous Control of Respiration. It is a matter of common

experience that one’s breath may be held for a short time, but the need

of fresh air speedily gets the mastery, and a long, deep breath is

drawn. Hence the efforts of criminals to commit suicide by persistent

restraint of their breathing, are always a failure. At the very worst,

unconsciousness ensues, and then respiration is automatically resumed.

Thus a wise Providence defeats the purpose of crime. The movements of

breathing go on without our attention. In sleep the regularity of

respiration is even greater than when awake. There is a particular part

of the nervous system that presides over the breathing function. It is

situated in that part of the brain called the medulla oblongata, and is

fancifully called the “vital knot” (sec. 270). It is injury to this

respiratory center which proves fatal in cases of broken neck.

From this nerve center there is sent out to the nerves that supply the

diaphragm and other muscles of breathing, a force which stimulates them

to regular contraction. This breathing center is affected by the

condition of the blood. It is stimulated by an excess of carbon dioxid

in the blood, and is quieted by the presence of oxygen.

Experiment 108. _To locate the lungs_. Mark out the boundaries of the

lungs by “sounding” them; that is, by _percussion_, as it is called.

This means to put the forefinger of the left hand across the chest or

back, and to give it a quick, sharp rap with two or three fingers. Note

where it sounds hollow, resonant. This experiment can be done by the

student with only imperfect success, until practice brings some skill.

Experiment 109. Borrow a stethoscope, and listen to the respiration

over the chest on the right side. This is known as _auscultation_. Note

the difference of the sounds in inspiration and in expiration. Do not

confuse the heart sounds with those of respiration. The respiratory

murmurs may be heard fairly well by applying the ear flat to the chest,

with only one garment interposed.

Experiment 110. Get a sheep’s lungs, with the windpipe attached. Ask

for the heart and lungs all in one mass. Take pains to examine the

specimen first, and accept only a good one. Parts are apt to be hastily

snipped or mangled. Examine the windpipe. Note the horseshoe-shaped

rings of cartilage in front, which serve to keep it open.

Experiment 111. Examine one bronchus, carefully dissecting away the

lung tissue with curved scissors. Follow along until small branches of

the bronchial tubes are reached. Take time for the dissection, and save

the specimen in dilute alcohol. Put pieces of the lung tissue in a

basin of water, and note that they float.

The labored breathing of suffocation and of lung diseases is due to the

excessive stimulation of this center, caused by the excess of carbon

dioxid in the blood. Various mental influences from the brain itself,

as the emotions of alarm or joy or distress, modify the action of the

respiratory center.

Again, nerves of sensation on the surface of the body convey influences

to this nerve center and lead to its stimulation, resulting in a

vigorous breathing movement. Thus a dash of cold water on the face or

neck of a fainting person instantly produces a deep, long-drawn breath.

Certain drugs, as opium, act to reduce the activity of this nerve

center. Hence, in opium poisoning, special attention should be paid to

keeping up the respiration. The condition of the lungs themselves is

made known to the breathing center, by messages sent along the branches

of the great pneumogastric nerve (page 276), leading from the lungs to

the medulla oblongata.