In plant life the permanent fabric consists of only three elements—carbon, hydrogen, oxygen. We know that plants alone convert inorganic or mineral substances into organic matter, and that plants as a necessary result assimilate their inorganic food, decompose carbonic acid, and restore its oxygen to the atmosphere.

Vegetation is constructed of cells or vesicles, and has a cellular tissue. A cell is a living organism. It is that which makes up the tissue of plants. For the whole life of the plant is that of the cells which compose it; in them and by them its products are elaborated, and all its vital processes are carried on. Cell multiplication by division, cell growth, cell modification, exist in plants. Fluids are transferred from cell to cell by a process called endosmose. Absorption takes place by the roots, and the substance absorbed is carried up into the leaves, even to the topmost bough of a tree, passing in its course many millions of apparently water-tight partitions. Plants exchange gases, taking in carbonic acid and giving off oxygen. They evolve heat, have organs of reproduction, and elaborate the material for the final evolution of the seed. This seed, whether of grain, of vegetables, or of fruits, is composed of carbon, hydrogen, and oxygen. And these constitute the starches and sugars which we find have been evolved by the vegetable or plant, and which form the food for animals. Plants, then, convert the elementary substances, the crude material, into food. In doing so, they pass through the processes known as the essentials of life; these are, birth, growth, development, decline, and death.

All organic compounds are transitory. They are constantly appearing and disappearing, composing and decomposing, organizing and disorganizing; and they are always dependent upon a certain degree of heat and moisture for their existence or non-existence.

The universal constituents of plant life; of organic existence, which are indispensable to vegetation, are carbon, hydrogen, oxygen, and nitrogen. Every vegetable substance is made up of at least eighty-eight to ninety-nine per cent of these elements. The proper vegetable structure, that is, the tissue itself, consists only of three of these elements, carbon, hydrogen, oxygen; while the fourth, nitrogen, is an essential constituent of the protoplasm, which plays so important a part in the formation of the cell, etc.

Plants prepare or elaborate out of these chemical elements food-substances composed of those elements—starches and sugars—upon which animals subsist. Animals feeding upon these vegetable substances assimilate, elaborate, them into meat substances, flesh, or proteids. These again are composed of carbon, hydrogen, nitrogen, and oxygen.

Nitrogen plays the important role in proteids, being the distinguishing feature, as contrasted with substances of vegetable origin, the carbohydrates.

Thus man is provided with two kinds of food: derived from plants, carbohydrates; derived from animals, proteids, or albumens, besides water and mineral salts.

These foods undergo certain preparations previous to being introduced into the system. In the system the food undergoes farther elaboration, to make it fit to enter into the circulation of the blood, in order to supply suitable material for the master tissues.

We will now examine briefly the organs and their secretions that convert food-substances into blood, and, by the blood, into tissue.

The solvents and diluents of food in the human animal economy are the saliva of the mouth, the gastric juice of the stomach, the pancreative juice of the pancreas, the bile of the liver, and the juices of the intestines—the succus entericus.

The digestive apparatus consists mainly of the alimentary canal together with various glands of which it receives the secretions.

The alimentary canal commences at the mouth and terminates at the anus. The average length is about thirty feet, about five or six times the length of the body.

The part situated in the head and thorax consists of the organs of mastication, insalivation, and deglutition, and comprises the mouth with the teeth, the salivary glands, and the Æsophagus or gullet. The parts contained in the abdomen and pelvis consist of the stomach and the small and large intestines.

The glands which are most immediately connected with digestion are very numerous small organs, situated in the mucous membrane of the alimentary canal, and the larger glands, such as the salivary glands, pancreas, and liver, whose ducts open on its inner surface.

The mouth is included between the lips and the throat, bounded by the lips, cheeks, tongue, and hard and soft palate. It communicates behind with the pharynx, and through the pharynx with the Æsophagus. It is lined throughout with mucous membrane.

The mouth contains 32 teeth, 16 in the upper jaw and 16 in the lower jaw. The inferior maxillary bone, or lower jaw, is the only movable bone about the head. The teeth have for their functions biting, grinding, chewing, or triturating any hard food substance that may be introduced into the mouth.

The tongue is a muscular organ covered with mucous membrane. By its muscular structure it takes part in the process of mastication and deglutition, and in the articulation of speech, while its mucous membrane, with common and tactile sensibility, is the seat of the sense of taste.

The tonsils are two prominent bodies which occupy the recesses formed, one on each side of the fauces, between the anterior and posterior palatine arches and the pillars of the fauces.

The saliva, which is poured into the mouth and there mixed with the food during mastication, is secreted by three pairs of glands named from their respective situation parotid, submaxillary, and sublingual.

The parotid is the largest of three salivary glands. It lies on the side of the face, in front of the ear, and extends deeply into the space behind the ramus of the lower jaw. Its weight varies from 5 to 8 drachms. It has a duct called the parotid or Stenson’s duct. It is about 2½ inches long, and about a line and a half in thickness. Its orifice is opposite the crown of the second molar tooth of the upper jaw.

The submaxillary gland weighs about 2 to 2½ drachms, and is situated on the inner surface of the inferior maxillary. The duct is named Wharton’s, and is about 2 inches in length. Its orifice is found under the tongue.

The sublingual gland weighs about a drachm. It is situated on the floor of the mouth. The ducts are called the ducti Rivintiani. They are from 8 to 20 in number. They may be seen when the tip of the tongue is lifted up.

Saliva. Mixed saliva, as it appears in the mouth, is a thick, glairy, generally frothy, turbid fluid.

The quantity of saliva secreted in 24 hours varies. The average amount is probably from two to three pints in 24 hours.

The composition of saliva is:

The solids are:

The specific gravity varies from 1.004 to 1.008.

The rate at which saliva is secreted is subject to considerable variation. When the tongue and muscles concerned in mastication are at rest, and the nerves of the mouth are subject to no unusual stimulus, the quantity secreted is not more than sufficient, with the mucus, to keep the mouth moist.

The purposes served by saliva are of several kinds:

1. Acting mechanically in conjunction with mucus, it keeps the mouth in a due condition of moisture, and facilitates the movements of the tongue in speaking, and the mastication of the food.

2. It serves also in dissolving sapid substances and rendering them capable of exciting the nerves of taste.

3. By mixing with the food during mastication, it makes it a soft pulpy mass, such as may easily be swallowed.

4. Saliva performs a chemical part in the digestion of food. It transforms starchy substances into dextrine and grape sugar.

Starch is a carbohydrate—carbon 18, hydrogen 30, oxygen 15.

Ptyaline is the salient feature of saliva. It is known as a ferment—acting upon starch and converting it into dextrine and grape sugar.

The action of saliva varies in intensity in different animals.

The food after having been acted upon and prepared is propelled, by the act of deglutition, through the Æsophagus into the stomach, by way of the pharynx.

The pharynx is that part of the alimentary canal which unites the cavities of the mouth and nose to the Æsophagus. It extends from the base of the skull to the lower border of the cricoid cartilage, and forms a sac open at the lower end, and imperfect in front, where it presents apertures leading into the nose, mouth, and larynx. The pharynx is about four and a half inches in length, and is considerably wider across than it is deep from before backwards.

The Æsophagus or gullet, the passage leading from the pharynx into the stomach, commences at the cricoid cartilage opposite the lower border of the fifth cervical vertebra, descends in front of the spine, passes through the diaphragm opposite the ninth dorsal vertebra, and ends by an opening at the cardiac orifice of the stomach. It is from nine to ten inches in length.

The stomach is situated in the abdominal cavity. It lies in part against the anterior wall of the abdomen, and in part beneath the liver and diaphragm, and above the transverse colon. It is somewhat conical or pyriform in shape. The left part is the larger, and is named the cardiac, or splenic, the right is named the pyloric, extremity. The upper border is about three or four inches in length, is concave, and is named the lesser curvature, while the lower border is much longer, is convex, and forms the greater curvature. The dimensions vary greatly in different subjects, and also according to the state of distension of the organ. When moderately filled, its length is about ten to twelve inches, and its diameter at its widest part from four to five inches. It weighs when freed from other parts about four and a half ounces in the male and somewhat less in the female.

The structure of the stomach consists of four coats—a serous, a muscular, an areolar, and a mucous coat. The external or serous coat is derived from the peritoneum. There are three kinds of muscular fibers—longitudinal, circular, and oblique, and the internal mucous lining is a rather thicker, soft, smooth, pulpy membrane, lying in ridges or rugÆ, and containing a large number of glands—tubular or gastric glands, and another variety of gland called peptic, besides others.

While the stomach contains no food, and is inactive, no gastric fluid is secreted; and mucus, which is either neutral or slightly alkaline, covers its surface. But immediately on the introduction of food into the stomach, the mucous membrane, previously quite pale, becomes slightly turgid and reddened with the influx of a large quantity of blood; the gastric glands commence secreting actively, and an acid fluid is poured out in minute drops, which gradually run together and flow down the walls of the stomach, or soak into the substance introduced. The quantity of this fluid secreted daily has been variously estimated; but the average for a healthy adult has been assumed to range from ten to twenty pints in twenty-four hours.

The specific gravity of gastric juice has been found to differ little from that of water, varying from 1.001 to 1.010, and the amounts of solid present to be very small, viz., about 56 per cent.

The chemical composition of gastric juice is:

On starch gastric juice per se has no effect whatever, nor has healthy gastric juice any effect on grape sugar or cane sugar. On fats gastric juice is powerless.

The essential property of gastric juice is the power of dissolving proteid matters (meats, albumens, nitrogenous substances), and converting them into a substance called peptones. Gastric juice thus readily dissolves coagulated proteids which otherwise are insoluble, or soluble only with difficulty in very strong acids.

Certain conditions are required for the perfection of the process, which are all found in the stomach. The first is a temperature of 100° F. Second, minute division and constant movement favor digestion. Third, the greater the surface presented to the action of the juice, the more rapid the solution.

Neutralization of the juice wholly arrests digestion.

The digestive action of gastric juice on proteids, like that of saliva on starch, is a ferment action; in other words, the solvent action of gastric juice is essentially due to the presence in it of a ferment body called pepsin.

The general effect of digestion of the stomach is the conversion of food into chyme, a substance of various compositions according to the nature of the food, yet always presenting a characteristic thick pultaceous grumous consistence.

The small intestines commence at the pylorus and after many convolutions terminate in the large intestines. They measure on an average about twenty feet in length in the adult. For convenience they have been divided into three parts—the duodenum, which extends from eight to ten inches beyond the pylorus; the jejunum, which occupies two-fifths, and the ilium, which occupies three-fifths, of the rest of the canal.

The mucous membrane, the interior coat, is the most important to the function of digestion. There are permanent folds, shelf-like processes, of the mucous membrane, called valvular conniventes. There are also villi and glands, as the glands of LieberkÜhn, of Peyer, and of Bruner. The glands of LieberkÜhn are thickly distributed over the whole surface of the large and small intestines. The glands of Peyer are exclusively in the small intestine. They are found in greatest abundance in the lower part of the ileum near to the ileo-cÆcal valve. They are met with in two conditions, viz., either scattered singly, in which case they are termed glandulÆ solitairÆ, or aggregated in groups varying from one to three inches in length and about half an inch in width, chiefly of an oval form, their long axes parallel with that of the intestines. In this state they are named glandulÆ agminatÆ. The latter are almost always placed opposite the attachment of the mesentery. In structure they are analogous to lymphatics or absorbent glands, and their office is to take up certain materials from the chyle, elaborate them, and subsequently discharge them into the lacteals, with which vessels they appear to be closely connected. Bruner’s glands are confined to the duodenum; they are most abundant and thickly set at the commencement of this portion of the intestines, and are provided with permanent gland ducts.

The villi are confined exclusively to the mucous membrane of the small intestines. They are minute vascular processes, from a quarter of a line to a line and two-thirds in length. There are about fifty to ninety in number to a square line. Each villus consists of a small projection of mucous membrane, and its interior is supported throughout by fine retiform or adenoid tissue. Two or more arteries are distributed to each villus, and from their capillaries, which form a dense network, proceed one or two small veins, which pass out at the base of the villus.

The lacteal vessels enter the base of each villus, and passing up in the middle extend nearly to the top, where it ends commonly by a closed and somewhat dilated extremity. The office of the villi is the absorption of chyle from the completely digested food of the intestines.

The large intestine extends from the termination of the ileum to the anus. It is usually about five to six feet in length, being about one-fifth of the whole length of the intestinal canal. The large intestine is constructed of four coats like those of the stomach and small intestines, namely, the serous, the muscular, the areolar or submucous, and the mucous. It is divided into the ascending colon, transverse and descending colon, and rectum and anus.

The cÆcum is a short wide pouch, communicating with the lower end of the small intestines through an opening guarded by the ileo-cÆcal valve. The appendix vermiformis is attached to the cÆcum. The colon commences at the right groin, ascends to the liver, forms the hepatic flexure, then crosses transversely from right to left to the spleen, forms the splenic flexure, descends to the left groin, forms the sigmoid flexure, passes through the pelvis as the rectum, and terminates at the anus.

The mucous membrane of the large intestines, like that of the small intestines, is lined throughout by columnar epithelium, but unlike it, is quite destitute of villi and is not projected in the form of valvular conniventes.

The peritoneum, or serous membrane of the abdominal cavity, is by far the most extensive and complicated of serous membranes. Like the others, it may be considered to form a shut sac, on the outside of which are placed the viscera, which it covers. The peritoneum forms the mesenteries and omenta for the stomach, small and large intestines, and ligaments for the liver, spleen, uterus, and bladder.

The liver is a very important glandular organ, very constant in the animal series, being found in all the vertebrates, and, in a more or less developed condition, in most invertebrate tribes. It secretes bile, and appears to act upon the blood which is transmitted through it. The liver is the largest gland in the body, and by far the most bulky of the abdominal viscera. It measures from ten to twelve inches transversely from right to left, between six and seven inches from its posterior to its anterior border, and about three and a half inches from above downwards where thickest, which is towards the right and posterior part. The average bulk is about eighty-eight cubic inches. The ordinary weight in the adult is between 50 to 60 ounces, about one-thirtieth of the weight of the whole body. The liver is solid to the feel, and of a dull reddish-brown color, with frequently a dark-purplish tinge along the margin. It has an upper surface smooth and convex, and an under surface which is uneven and concave. The liver is divided into two unequal lobes, a right and a left, and on the under surface of the right lobe are three secondary lobes or lobules, named the lobe of Spigolius, the caudate or tailed lobe, and the square lobe. It has five fissures or fossÆ, described as the transverse or portal; the umbilical fissure and the fissure of the ductus venosus, together forming the longitudinal fissure; the fossa of the vena cava, and the fossa of the gall bladder. It is held in position by five ligaments formed by layers of peritoneum.

The liver is situated on the right side of the body under the diaphragm. The convex surface is protected, on the right by the six or seven lower ribs, and in front by the cartilages of the same, and by the ensiform cartilage, the diaphragm of course being interposed.

To the left of the longitudinal fissure the liver is in contact with the pyloric extremity and anterior surface of the stomach, on which it moves freely. When the stomach is quite empty, the left part of this surface of the liver may overlap the cardiac end of that organ. To the right of the longitudinal fissure the liver rests upon the first part of the duodenum and the hepatic flexure of the colon. Farther back it is in contact with the upper part of the right kidney and suprarenal capsule.

The two blood-vessels which supply the liver are the hepatic artery and the vena porta. The hepatic vein conveys the blood away from the liver.

The lymphatics of the liver are large and numerous, forming a deep and a superficial set.

The nerves are derived partly from the coeliac plexus and partly from the pneumogastric nerve, especially from the left pneumogastric.

The excretory apparatus of the liver consists of the hepatic duct, the cystic duct, gall bladder, and common bile duct.

The hepatic duct is formed by the union of a right and left branch, which issue from the bottom of the transverse fissure and unite at a very obtuse angle; it descends to the right, within the gastro-hepatic omentum. Its diameter is nearly two lines, and its length nearly two inches. At its lower end it meets the cystic descending from the gall bladder, and the ducts uniting together at an angle form the common bile duct.

The cystic duct is about one and a half inches in length.

The gall bladder is a pear-shaped membranous sac, three or four inches long, about an inch and a half across its widest part, and capable of containing from 8 to 12 fluid drachms. The gall bladder is attached to the liver. The neck, gradually narrowing, becoming constricted, bends downward, and terminates in the cystic duct.

The common bile duct (ductus communis choledicus), the largest of the ducts, being from two to three lines in width, and nearly three inches long, conveys the bile from the liver and the gall bladder into the duodenum by a common orifice, with the pancreatic duct on its inner surface, about three to four inches below the pylorus.

The liver is an extremely vascular organ, and receives its blood supply from two distinct vessels, the portal vein and the hepatic artery, while the blood is returned from it into the inferior vena cava by the hepatic vein. Its secretion, the bile, is conveyed from it by the hepatic duct, either directly into the intestines, or, when digestion is not going on, into the cystic duct, and thence into the gall bladder, where it accumulates until required. The portal vein, hepatic artery, and hepatic duct branch together throughout the liver, while the hepatic vein and its tributaries run by themselves. At the transverse fissure it is merged into the areolar investment called Glisson’s capsule, which surrounds the portal vein, hepatic artery, and hepatic duct, as they enter at this part, and accompanies them in their branches through the substance of the liver.

The liver is made up of small roundish or oval portions called lobules, each of which is about 1/20? of an inch in diameter, and composed of minute branches of the portal vein, hepatic artery, hepatic duct, and hepatic vein; while the interstices of these vessels are filled by liver cells. These cells, which make up a great portion of the substance of the organ, are of rounded or polygonal form; about 1/800? to 1/1000? of an inch in diameter.

The function of the liver is the secretion of bile. The bile is a somewhat viscid fluid of a yellow, or greenish-yellow, color, a strongly bitter taste, and when fresh a scarcely perceptible odor. It has a neutral or slightly alkaline reaction, and its specific gravity is 1.020.

The composition of human bile is:

The solids are:

Bile is distinguished from the other alimentary secretions by the entire absence of proteids. The chemical composition of bilin, as compared with the organic parts of blood, is:

There seems to be some relationship between the coloring matters of the blood and bile; and it may be added, between these and that of the urine also; so that it is possible they may be, all of them, varieties of the same pigment, or derived from the same source.

The quantity of bile discharged into the intestines is estimated to be about thirty to forty ounces secreted by an adult man in twenty-four hours.

The purposes served by the secretion of bile may be considered to be of two principal kinds, viz., excrementitious and digestive.

As an excrementitious substance, the bile serves especially as a medium for the separation of excess of carbon and hydrogen from the blood.

Though one of the chief purposes of the secretion of bile may appear to be the purification of the blood by ultimate excretion, yet there are many reasons for believing that while it is in the intestines it performs an important part in the process of digestion. Bile has a slight solvent action on fats, and only a slight emulsifying power.

Its functions generally may be considered thus:

1. It assists in emulsifying fatty portions of food, thus rendering them capable of being absorbed by the lacteals.

2. Bile facilitates the absorption of fatty matter.

3. Bile, like the gastric fluid, has a strongly antiseptic power, and may serve to prevent the decomposition of food during the time of its sojourn in the intestines.

4. Bile has been considered to act as a natural purgative, by prompting an increased secretion of the intestinal glands.

5. Another very important function appears to be that of so acting upon certain constituents of the blood passing through it, as to render some of them capable of assimilation with blood generally, and to prepare others for being duly eliminated in the process of respiration.

6. An important influence seems also to be exerted by the liver upon the saccharine matters derived from the alimentary canal. The chief purpose of the saccharine and amylaceous principles of food is, in relation to respiration and the production of animal heat.

The pancreas is a long, narrow, flattened gland of a reddish-cream color, larger at one end than at the other, and lying behind the stomach opposite the first lumbar vertebra. It is usually from 6 to 8 inches long, about 1½ inch in average width, and ½ to 1 inch in thickness. It weighs about 2¼ to 3½ ounces. Its principal excretory duct is called the pancreatic duct, and runs through the entire length of the gland from left to right. The duct opens in a common orifice with the ductus communis choledicus on the inner surface of the duodenum about 4 inches below the pylorus.

Healthy pancreatic juice is a clear, viscid fluid, frothing when shaken. It has a very decided alkaline reaction. The pancreas in its minute anatomy closely resembles the salivary glands; and the fluid elaborated by it appears almost identical with saliva.

The composition of pancreatic juice is:

The solids are:

Action of pancreatic juice. (1) It acts on starch raw and boiled with great energy, rapidly converting it into grape sugar. (2) On proteids (meats) it also exercises a solvent action, so far similar to that of gastric juice that by it the proteids are converted into peptones. (3) On fats pancreatic juice has a twofold action: it emulsifies them, and it splits up neutral fats into their respective acids and glycerine.

Thus pancreatic juice is remarkable for the power it possesses of acting on all food-stuffs—on starch, fats, and proteids.

Succus entericus (intestinal juice). The precise action of this is not known. It has been said to act upon starch, to convert proteids into peptones, and to emulsify fats. On the other hand, each of these actions has been denied.

The portal system of veins. The portal vein, or vena porta, collects the blood from the stomach, intestines, pancreas, and spleen; and carries it to the liver, from which the bile is secreted; ramifying after the manner of an artery in the substance of the liver and conveying to the capillaries of that organ the blood collected in the main trunk. This blood, together with that of the hepatic artery, after having served for the secretion of the bile and the nourishment of the liver, is withdrawn from that organ by the hepatic veins, and carried by them into the vena cava inferior.

Digestion begins at the mouth. Food is masticated by the movement of the lower jaw, broken into small pieces, moistened by the saliva, and starchy substances are converted into sugar. No change takes place during the rapid transit through the Æsophagus.

In the stomach the proteids are acted upon by the gastric juice and converted into peptones. Fats remain unchanged, and sugars are not acted upon. While these changes are proceeding, the thick grayish liquid, or chyme, formed by the imperfectly dissolved food, is from time to time ejected through the pylorus, accompanied even by large morsels of solid less digested matter. This may occur within a few minutes of food having been token, but the larger escape from the stomach probably does not begin till from one to two and lasts from four to five hours after the meal, becoming more rapid towards the end, such pieces as most resist the gastric juice being the last to leave the stomach. Substances can be absorbed from the cavity of the stomach into the circulation. The presumption is, that the diffusible sugars and peptones pass by osmosis direct into the capillaries, and so into the gastric veins.

In the small intestines the semi-digested food, or chyme, as it passes the biliary orifice causes a gush of bile, and at the same time the pancreatic juice which flows freely into the intestine at the taking of the meal, is secreted again with renewed vigor, when the gastric digestion is completed. The conversion of starch into sugar, which may have languished in the stomach, is resumed with great activity by the pancreatic juice. The pancreatic juice emulsifies fats, and also splits them into their respective fatty acids and glycerine, and the bile is able to a certain extent to saponify the free fatty acids. It also appears that the slight emulsifying power of the bile is much increased by the presence of soap; and as a matter of fact, the bile and pancreatic juice do largely emulsify the contents of the small intestines, so that the grayish turbid chyme is changed into a creamy-looking fluid, which has been called chyle. These products as they are formed pass into the lacteals or the portal blood-vessels.

Through the large intestine pass off indigestible or undigested constituents of the meal, and the gases generated.

Absorption takes place from the stomach, and occurs along the course of the small and large intestines, especially of water. The largest and most important part of the digested material passes away from the canal during the transit of food along the small intestines, partly into the lacteals, partly into the portal vein.

Digestion being, broadly speaking, the conversion of non-diffusible proteids and starch into highly diffusible peptones and sugar, and the emulsifying, or division into minute particles, of various fats, it is natural to suppose that the diffusible peptones and sugars pass by osmosis into the blood-vessels, and that the emulsified fats pass into the lacteals. That the great mass of the fat which enters the body from the intestines passes through the lacteals, there can be no doubt; and there is but little doubt that a considerable quantity of peptone and sugar does pass into the portal blood.

Chyle is a white milky-looking fluid, which after its escape coagulates, forming a not very firm clot. The nature of the coagulation seems to be exactly the same as that of blood.

Lymph seems to be blood minus red corpuscles, and chyle is lymph plus a very large quantity of minutely divided fats.

It has been calculated that a quantity equal to that of the whole blood may pass through the thoracic duct in twenty-four hours, and of this it is supposed that about half comes from food through the lacteals, the remainder from the body at large; but these calculations are based on uncertain data.

Entrance of chyle into the lacteals. The lacteals begin at a club-shaped lymphatic space lying in the center of the villus, and connected with the smaller lymphatic spaces of the adenoid tissue around it; it opens below into the submucous lymphatic plexus from which the lacteals spring.

The thoracic duct is the common trunk which receives the absorbents from both the lower limbs, from the abdominal viscera, from the walls of the abdomen, from the left side of the thorax, left lung, left side of the heart, and left upper limbs, and from the left side of the head and neck. It is from fifteen to eighteen inches long in the adult, and extends from the second lumbar vertebra to the root of the neck. At the last dorsal vertebra there is usually a dilation of the duct, of variable size, which is called the receptaculum chyli, and is the common place of junction of the lymphatics of the lower limbs and the trunks of the lacteal vessels. There are two sets of absorbent vessels—the lacteals, which convey the chyle from the alimentary canal to the thoracic duct; and the lymphatics, which take up the lymph from all the other parts of the body and return it into the venous system. There is a right lymphatic duct, about a quarter to a half inch in length, which receives the lymph from the absorbents of the right upper limb, the right side of the head and neck, the right side of the chest, the right lung and the right half of the heart, and the upper surface of the liver. The thoracic duct terminates on the outer side of the internal jugular vein, in the angle formed by the union of that vein with the subclavian, and the subclavian empties itself in the superior vena cava.

Lymphatics and lacteals are furnished with valves serving the same office as those of the veins, and for the most part constructed after the same fashion.

Lymph and chyle, unlike the blood, pass only in one direction, namely, from the fine branches to the trunk and so to the large veins, on entering which they are mingled with the stream of blood and form part of its constituents.

In some part of their course all lymphatic vessels pass through certain bodies called lymphatic glands.

Analysis of lymph and chyle:

Chyle having reached the lymphatic channels, its onward progress is determined by a variety of circumstances. Putting aside the pumping action of the villi, the same events which cause the movement of the lymph generally, also further the flow of the chyle, and these are briefly as follows:

1. The wide-spread presence of valves in the lymphatic vessels causes every pressure exercised on the tissues in which they lie, to assist in the propulsion forward of the lymph.

2. Considering the whole lymphatic system as a set of branching tubes passing from the extravascular regions just outside the small arteries and veins and capillaries, to the large venous trunks, it is obvious that the mean pressure of the blood in the subclavian at the junction with the jugular is the cause of the movement, etc., assisted perhaps by the respiratory movements, and other causes, as osmosis, etc.

The average quantity of solid fecal matter evacuated by the human adult in twenty-four hours is about five ounces; an uncertain proportion of which consists simply of the undigested or chemically modified residue of the food, and the remainder of certain matters which are excreted in the intestinal canal.

Gases contained in the stomach and intestines. The sources of the gases contained in the stomach and bowels may be enumerated:

1. Air introduced in the act of swallowing either food or saliva.

2. Gas developed by the decomposition of alimentary matter, or of the secretions and excretions mingled with it in the stomach and intestines.

3. It is probable that a certain mutual interchange occurs between the gases contained in the alimentary canal, and those present in the blood of the gastric and intestinal blood-vessels.

The movement of the intestines is peristaltic or vermicular, and is effected by the alternate contractions and dilatations of successive portions of the intestinal coats. The contractions, which may commence at any point of the intestine, extend in a wavelike manner along the tube. This is due to the involuntary longitudinal and circular muscular fibers contracting successively from above downwards and from behind forwards, etc. The movements take place slowly, and in health are commonly unperceived by the mind, but they are perceptible when they are accelerated under the influence of any irritation.