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A MANUAL OF HEALTH.

CHAPTER III.

DIGESTION, AND THE ORGANS BY WHICH IT IS
PERFORMED.

B

which, is carried on in every part of sponges, animalcules, and polyps, is performed by gills in crabs and lobsters and fishes, and by lungs in land-breathing animals and man.

In man and the higher animals, the food, before it is converted into blood and applied to the uses of the system, undergoes an elaborate series of changes. It is first taken into the mouth, and that food which is not liquid undergoes the process of mastication. For this purpose the mouth is supplied with teeth. These organs have a different structure, according to the food they have to act on. In herbivorous animals the teeth have broad surfaces, as in the sheep, ox, and horse, for the purpose of enabling them to triturate their food before it enters the stomach.

EFORE the food of an animal can be appropriated to the use of its body it is submitted to various operations, by which it is fitted to become the means and source of life. In the lowest animals this process is of the simplest kind. Amongst the animalcules are creatures which consist merely of a bag or stomach, into which the food is carried, and, by a simple process of absorption, the food passes These teeth are called grinders. into the structure of the body, and performs all the functions of life; in fact, the lowest animals Animals such as the lion, the tiger, cats and consist of merely a bag or stomach, into which dogs, which live principally on animal food, the food is taken, and the nourishing and vital have cutting teeth, whilst in man, who is parts of the food being taken into the surround-destined to live on a mixed diet, the two sorts of ing parts, the useless constituents of the food teeth are found. The human infant is born are rejected by the same orifice in which they are taken in. Such is the structure of hydras, sea-anemones, jelly-fishes, polyps, and other low forms of animals. As we ascend in the scale of organization we meet with animals in which a higher structure is present. The food is received into a bag or stomach, and soaks through from thence into a circulatory system of fine tubes, where it becomes a part of that fluid known as the blood. The food of all animals undergoes certain changes in contact with the oxygen of the air, which is necessary for their life; and this function, which goes on all over the body in the lower animals, is carried on in special organs in the higher animals. In fact, as we ascend from the lower to the higher animals, we find that particular organs are assigned for the porformance of special operations or functions. Thus, the oxidation of the food,

without teeth, but at the sixth month they begin to appear, and by the end of the fourth year twenty teeth appear. These are called the milk teeth, and are destined to disappear and make way eventually for thirty-two teeth, which are sometimes not fully developed until the human being has reached the age of from sixteen to twenty-five years. These teeth consist of eight teeth in front, like chisels in shape, four in the upper jaw and four in the lower, they are called incisors. On each side of these above and below, is a cutting tooth, like those of lions and tigers, called a canine tooth. Beyond these, on either side, are five grinding teeth, called molars, this making altogether thirty-two teeth. It is between these cutting and grinding teeth that the food is first prepared before being carried into the stomach for digestion.

Whilst the process of mastication is being

carried on, the food is mixed with a fluid in the villi, like the "pile" on velvet. They consist of mouth, called saliva or "spittle." This fluid is small blood-vessels and a duct, which last abexuded from organs, called glands, seated on sorbs the fluid chyle, and carries it into a netthe sides of the lower jaw, and which empty work of minute vessels outside the bowels called their contents into the mouth. Saliva is con- lacteals, whilst the blood-vessels also soak up stantly being thrown into the mouth, and the some of the liquid. The milky fluid in the glands which produce it are stimulated to action lacteals is carried into a larger vessel called the by substances taken into the mouth. Thus, thoracic duct, which empties itself into the tobacco smoke stimulates these glands, and blood of the veins in the upper part of the engenders in those who smoke the injurious chest very near the heart. In passing from the habit of spitting. The saliva contains an active stomach along the bowels, a large proportion of principle, called salivin, which, mixing with the the liquid contents of the chyle is taken directly starch of food, converts it into sugar. The into the minute blood-vessels which line the process in which the saliva is so mixed with the inner membrane of the stomach and bowels, but food is called insalivation, and it is most neces- the blood in these does not go at once to the sary to healthy digestion that all food contain- heart to be sent by it all over the body, but, as ing starch, such as bread, flour puddings, arrow- we shall see, it has first to pass through the liver, root, and corn flour, should be thoroughly well where the absorbed food is more thoroughly insalivated before it is swallowed. made into blood. The undigested parts of the food are carried along the bowels and are ultimately rejected.

When food is masticated and insalivated it is swallowed. This process is technically called deglutition. The tongue is employed in this The ultimate object of the function of process, and the food having been formed into digestion is the preparation of the food for being a lump or bolus by the action of this organ, is absorbed and converted into blood. Although transferred to the back of the throat. Here it amongst the lower animals, little or no preparais received by a bag, called the pharynx, which tion of the food before being masticated is found by its muscular action propels the food down necessary, it is owing to the characteristics of the gullet into the stomach. This again is a bag, man that he is a “cooking animal," and that consisting of a muscular coat, capable of acting previous to eating it, he submits a large proporon and propelling the food like the pharynx and tion of his food to heat. This is found to aid gullet; its interior is lined with a mucous mem- greatly in the process of digestion, and facilibrane, in which are placed certain glands which tates the conversion of food into blood. Food have the power of secreting an acid juice, which is cooked either by placing it in contact with is called gastric acid or juice. This juice, like heated air or heated water. The former process saliva, contains an active principle called pepsin, is called baking or roasting, the latter boiling. which acts more particularly on the flesh-form- Animal and vegetable foods are submitted to ing constituents of the food, and converts them either of these processes. Wheaten flour is from substances incapable of solution in water mixed with water, and then fermented with into soluble substances, called peptones. The yeast and submitted to heat, and is then called flesh-forming substances, such as meat, albumen, and casein, are all converted into the same soluble matter, which readily soaks through the wall of the stomach into the blood-vessels. The food in the stomach not dissolved is converted into a pasty mass. This mass moves from one end of the stomach to the other, and passes into the bowels through an orlfice called the pylorus.

leavened bread. When flour is not fermented, biscuits of various kinds are produced and form unleavened bread. By the process of leavening, the bread is vesiculated by the particles of carbonic acid gas, produced by the leaven, and it is thus made light and is more easily digested than unleavened biscuits. Bread is sometimes made light by pumping into it atmospheric air, which vesiculates it in the same way as yeast, and it is then called "aerated" bread.

The food having passed the pylorus, is subject to the action of two other fluids-one coming Animal food is also baked and roasted; by from the liver, called bile, and another from the this means the little cells and fibres of which pancreas, catled pancreatic juice. These two animal flesh is composed are broken up, and fluids are poured together into the bowels a few they are more readily digested than raw meat inches below the pylorus. The result of the would be. In baking or roasting, care should mixture of these fluids with the pasty mass or be taken to expose the meat to a strong heat at chyme is the production of a milky liquid matter once; this has the effect of coagulating the called chyle. It consists of the dissolved sugar albumen which is contained in the meat, and and peptone, and minute particles of fatty matter which thus forms a kind of impermeable case suspended in water. All over the interior of round the baking or roasting meat, and prevents the bowels are a number of minute points called the juice from the interior of the meat from run

ning away. This juice contains the flavoring ous animals take larger quantities of food and matter of the meat, as well as other chemical are longer in digesting it than carnivorous anicompounds which, acting on the mouth and mals. Man is an omnivorous animal, and stomach, influence beneficially the process of whilst he can exist either entirely on animal digestion. It is on this account that small food, or on vegetable products only, he unquantities of animal food are better than none, doubtedly flourishes best on a mixed diet. An and act more advantageously than equivalent examination, also, of the structure of his teeth, quantities of vegetable food. stomach, and bowels show that he is adapted to In boiling animal food, the same principle take a mixture of animal and vegetable food. should be recognized as in baking or roasting. Under these circumstances man is found taking The animal or joint should be first placed in his meals several times a day, and there is no boiling water till a case of coagulated albumen doubt that he digests his food better by taking is formed outside. When this is formed, the it twice than once a day, and three times better heat may be reduced and the meat cooked at a than twice. It seems a most natural arrangesomewhat lower temperature. In all cases ment that he should take breakfast, dinner, and where animal food is boiled, it should be recol-supper. Breakfast should be taken from half lected that certain quantities of the flavoring an hour to an hour after rising. Dinner or and saline principles of the meat are dissolved luncheon four or five hours after breakfast, and in the water. These may be made available for supper or dinner five or six hours after the food by converting the water thus employed into soup. The use of soup as an article of diet is much neglected. Many portions of animal food which can not be served up separately, may be made into soup which, thickened with the flour of wheat, barley, oats, peas, lentils, maize, rice, or potatoes, and flavored with condiments, form excellent food. All articles of diet containing starch are thickened or even made solid by boiling. Thus flour and water are mixed and made into a paste, which, by boiling, become converted into "dumplings." Eggs mixed with flour and various other things, form "puddings" by the process of boiling.

middle-day meal. It is never well to protract the last meal to within a short time of going to bed. A full stomach interferes with the action of the heart, and blood-vessels, and lungs, when the body is in a horizontal position. Time should also be given to the taking of food, and meals should be taken sitting, and at least halfan-hour should be given to each meal.

CHAPTER IV.

THE NATURE OF THE BLOOD, AND ITS CIRCULA-
TION BY THE HEART.

The food, after being dissolved, is taken up It is very desirable that all cooked food into the blood-vessels, either directly or through should be taken hot. When cold food is taken the lacteals, and is the great means of the it reduces the temperature of the stomach, and renewal of the blood. This, however, is not both the nerves and vessels of the stomach are the only fluid which enters the blood, and serves taxed in order to bring the temperature of the for its production. Throughout the whole body food thus taken up to that of the human body. there exists, besides the fine network of bloodMankind in all ages seems to have discovered vessels, a network of minute vessels, called that it is desirable to prevent this tax upon the lymphatics, and which join the thoracic duct internal organs, and have taken their food hot like the lacteals. They contain a clear fluid, in order to prevent it. It was death to the which is called lymph, and is derived from the Roman slave to bring in his master's water various parts of the body to which these vessels tepid or cold, so much importance did they are distributed. Just as the blood-vessels and attach to hot water as drink. We drink tea, lacteals of the bowels take up the liquid food, coffee, and chocolate hot, and these substances so do the lymphatics and the blood-vessels in are added to water in order to flavor it which is muscles and nerves and bones take up the a necessity of the system. It should, then, be liquids which these turn into as they die and recollected that a hot meal is a great economy waste away, in doing their work. In the lower compared with a cold one, and that, as a rule of animals the blood is generally free from color, life, it is better to consume food hot rather than like lymph; but as we ascend in the scale of cold. It is only in very hot weather in temper- organization the blood gradually becomes opaque, ate climates, or in tropical climates, that food and in fishes, reptiles, birds, the mammalia, and can be taken with advantage when cold, or that man, it is red. ice and iced drinks can be taken with impunity. The blood of man, when drawn and looked Not only should food be properly prepared at with the naked eye, is a red liquid. When before it is eaten, but it should be taken at allowed to stand for a few minutes it "coaguproper times. Vegetable food requires a longer lates," and is separated into two parts-a solid time to digest than animal food, and herbivor-part, which is called clot, and a liquid part, in

which the clot floats, and which is called serum. body. Whilst in the lungs, it takes up oxygen If a drop of blood is placed under a microscope gas, but throws off carbonic acid gas, which is before it coagulates it is found to consist of two injurious to the body. In the liver it gets rid of parts-a liquid, called "liquor sanguinis," and a certain products which form the bile, and which number of small flattened globules or cells, appear to be again taken up into the blood in which are called blood globules. The latter are the bowels. In the kidneys it gets rid of a. of two kinds, red and white. The white globules substance called urea, which, like the albumens, are rounder, rougher, and larger than the red is formed of all four of the organic elements, ones; they differ further in containing a more and represents these substances in a changed solid central part or kernel, and do not form and effete form, by which they are thrown out more than one in a hundred of the blood- from the body. globules altogether, though the lymph is full of The organs by which the blood is carried all them. Their "kernels" or nuclei are supposed through the body are called a circulatory systo escape and become red globules. The red tem. In the lower animals this system consists globules are very minute, and when measured of a simple open vessel, situated between the are found to be 1-3500th of an inch in diameter: stomach and skin, which contains an uncolored that is, 3500 of these minute bodies could be fluid, the result of the direct conversion of the placed side by side on a single linear inch. food into a nutritious material. In insects, this These red globules are depressed both above simple vessel presents certain dilatations, which and below, and in man and those animals which expand and contract, and send the fluid blood suckle their young, have no kernel; but in through all parts of the body. Passing upwards, birds and reptiles and fishes they have one. through fishes and reptiles, these bags become The red globules are composed of a red sub- more complicated in their structure, and form stance called hemoglobin, which can be sepa what is called a heart. In birds, the mammalia, rated into an albumen called globulin, and a and man, the heart consists of four cavities, coloring matter, which gives the thin red color, which are all bound together to form one organ, and is called hæmatin. The size and shape of called a heart. The structure of this organ can the blood-globules varies in different animals. be best understood by taking the heart of a In sheep, oxen, and deer, they are smaller than sheep or bullock, and cutting it up with a pair in man, and are much larger in repliles; they of scissors, when the four,cavities can be easily are oval in birds and fishes. A knowledge of the forms of the blood-globules has sometimes led to the detection of crime by revealing the exact nature of blood-stains found upon clothes after the commission of crime.

discerned.

The heart in the higher animals and man is divided into a right and left side, or a right and left heart. Each of these has two cavities. One of these cavities is called an auricle, the The liquor sanguinis consists of water, albu- other a ventricle. They are all composed of mens, and saline matters. When blood coagu- muscular fibres, which are so arranged that lates, an albuminous body which has been called when the muscles contract the cavities become blood-fibrin is formed, and separates, entangling shrunk, and the blood which they contain is the blood-globules, and constitutes the clot. pressed out of them. The auricles are thinner The serum which is left holds in solution most and less powerful than the ventricles, and the of the albumens and saline matters. The serum ventricle of the right side is of less size and also contains various other matters, such as weaker than on the left. In man, the heart is coloring and odoriferous principles, with dis- placed a very little to the left of the thorax, and solved fatty matters. The proportions of these its pulsations may easily be heard by placing the substances in 100 parts of dead blood is as fol- ear on the left side of the chest. The right lows:-Water 79 parts, albumens 4, globules 14, auricle receives into it the blood which flows fibrin one-fifth, and the salts and other principles along the great veins from the head and lower two and four-fifths. It also contains oxygen parts of the body. The blood having flowed and nitrogen gases, carbonic acid and a little into the auricle it contracts, and forces the blood ammonia. Thus constitued, it is carried by into the ventricle. The ventricle contracting, means of the heart and arteries to all parts of propels the blood through the large bloodthe body. On coming in contact with the deli- vessels called the pulmonary arteries, through cate structures of the body it supplies them which it passes into the lungs. The right side with new materials by which they perform their of the heart is hence called the pulmonic heart, various functions, and carries away those parti- because it forces the blood into the lungs. cles which have done their duty in the work of Whilst passing through the lungs, the blood is life. In its course through the body it is carried exposed to the action of the atmospheric air, to various glands, which separate from it those and becomes changed in color from a dark color compounds which are to be thrown off from the to a bright red. The dark blood is called venous

blood, as it has been brought to the lungs from spaces, consisting of the various textures of the the veins; the bright red blood is called arterial body. The walls of the capillaries are so thin blood, as it passes from the lungs to the left and soft, that they admit of the fluid parts of heart, and is thence distributed by this organ the blood soaking through them, and thus a through blood-vessels called arteries to the perfect communication exists between them and whole of the body. The left heart is hence the textures of the body in which they are called the systemic heart. The blood passes placed. The arteries then, coming from the from the lungs by the pulmonary veins to the left side of the heart, terminate in capillary vesleft auricle of the heart, which, when the blood sels, and it is through these that the blood arrives, contracts and sends it into the left ven- passes to that set of vessels which go back to tricle; from this cavity, which is the strongest the right side of the heart, and are called the and most powerful of all the cavities of the veins. In the capillary vessels the chief work heart, it is sent into the great aorta, a large of the blood is done. It is here, as we have blood-vessel which runs first upwards, then seen, that those intercharges between the blood curves round and runs straight down along the and the tissues take place, which are necessary interior of the body, giving off in its course for the nourishment of the body and the carrynumerous branohes, by which the living stream of the blood is conveyed to all parts of the body.

ing on of the various functions of life. In these minute vessels those changes take place which result in. what is called "inflammation," The blood is carried by the aorta and its and it is from the unhealthy action of the capilbranches to the head, to the arms, to the stomach laries that those deposits are made in the tissues and bowels, to the liver and kidneys, to the legs, which result in some of the most fatal diseases and all other parts of the body. It courses to which human beings are subject. Some of along blood-vessels, all of which are called these diseases are familiarly known as cancer, arteries. These blood-vessels are seated deeply scrofula, and tubercles of the lungs, or conin the textures of the body, and are composed sumption. The blood coming from the left of an elastic fibrous membrane, which yields to side of the heart contains more oxygen than each separate impulse of the heart, and which, that going to the right. It is during its passage in some places, as in the neck, can be seen with through the capillaries of the body that it loses the eye, and in some parts can be felt with the a portion of its oxygen, which is used up in finger. The beating of the arteries, produced" oxidizing" the tissues. by the contraction of the heart on the blood, is The blood, having passed through the capilcalled the pulse. When the ear is applied to laries, goes to the veins, and from them is conthe chest over the region of the heart, two veyed to the right side of the heart. The coats sounds are heard, the first a longer and duller of the veins are thinner than the arteries, and, sound than the second, which is sharp and when empty, they collapse, but an artery remains short. These sounds result from the quick tubular after it has been emptied of its contents. movement of flaps of membrane inside the The veins are usually placed on the surface of heart, which are pressed against by the blood the body, and can be seen carrying the dark when the heart contracts, and so prevent it from blood on the backs of the hands, on the arm, going the wrong way. The pulse is the result of and in the neck. The veins, in carrying up the the contractions of the heart, and equals them blood from the lower parts of the body, have a in number. The pulse varies much in fre- difficult task to perform; and when their interquency, according to age, health, and other cir-nal structure is examined, it is found that they cumstances. Seventy beats in a minute may be are assisted in this work by a series of valves. regarded as the ordinary number of a healthy These valves are placed directly across the veins, man. It is much quicker in infants and chil- and allow the blood to go onwards, but predren, and slower in old age. It is quicker in vent its going back; they act, in fact, like women than in men, and beats more frequently ordinary flood-gates, which allow the water to in an erect position than in lying down, and is go through in one direction, but shut when it more rapid during exercise than when persons attempts to flow the other way. It was the are resting. observation of these valves that led Harvey to The arteries terminate in delicate networks of the discovery of the circulation of the blood. small blood-vessels, called capillaries. They He felt sure that the blood must go on in the are called so from their resembling a hair veins into the heart; and although he never saw (capilla). They are, however, finer than any it passing through either the capillaries of the hairs, varying from the five thousandth to the lungs, or the system, he felt himself justified in fifteen hundredth part of an inch in diameter. asserting that the blood passes constantly from Between these capillaries, which are looped one side of the heart, round by the body or together and form a network, are minute inter-lungs, to the other. By the aid of a microscope,

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