Chapter X

THE ABDOMEN AND THE ORGANS OF DIGESTION AND EXCRETION.

=The Abdominal Cavity.=--Below the diaphragm and separated from the lowest cavity of the trunk, the pelvis, only by an invisible plane drawn through the brim of the true pelvis, is the abdominal cavity, which may be said in a general way to contain the organs of digestion and the kidneys. It is protected behind by the vertebræ and anteriorly by the lower ribs above and below by muscular walls, which make possible the complete bending of the body. These muscles are for the most part large and very strong and the greater number are inserted, in part at least, into a median tendinous line, the _linea alba_, which passes from the ensiform cartilage of the sternum above to the symphysis pubis below.

=Muscles.=--The _external oblique muscles_ form the outermost layer of the abdominal wall. They rise from the external surface of the eight lower ribs on either side and are inserted in the anterior half of the iliac crest as well as by aponeurosis in the linea alba, where each joins its fellow from the opposite side, the fibers running downward and inward like the fingers in the trouser’s pocket. Along the lower border of the aponeurosis is a broad fold, _Poupart’s ligament_. The _internal oblique_ rises on either side from the outer half of Poupart’s ligament and the anterior part of the crest of the ilium and is inserted into the crest of the os pubis, the cartilages of the lower ribs, and the linea alba. Its fibers run at right angles to those of the external oblique. These oblique muscles serve to compress the viscera, to flex the body, and also assist in expiration.

The deepest of the abdominal muscles is the _transversalis_, which rises from the outer third of Poupart’s ligament and the adjoining part of the crest of the ilium, from the six lower costal cartilages, and by a broad aponeurosis, the _lumbar fascia_, from the lumbar vertebræ. It is inserted into the pubic crest and by aponeurosis into the linea alba. There is one of these muscles on either side.

The _rectus abdominis_ is also really two muscles and extends from the symphysis pubis to the cartilages of the fifth, sixth, and seventh ribs. At first it passes back of the oblique and transversalis muscles, but about a fourth of the way up it passes in front of the transversalis and between two layers of the internal oblique, which thereafter forms its sheath. Its chief duty is to flex the chest on the pelvis, though it also compresses the abdominal viscera.

One other muscle, a small one, is found in front, the _pyramidalis_, which rises from the pubic crest and is inserted into the linea alba midway to the umbilicus.

At the back the open space over the kidneys, between the lower ribs and the os innominatum, is closed in on either side by the _quadratus lumborum_, which extends from the three or four lower lumbar vertebræ and the adjacent iliac crest to the last rib and the upper four lumbar vertebræ. It flexes the trunk laterally or forward according as one muscle or both are used, and may aid in either expiration or inspiration.

The _nerves_ of the abdominal muscles are chiefly the internal intercostals.

=The Peritoneum.=--Lining the abdominal cavity is a serous membrane, the peritoneum, which is reflected back over the viscera within in such a way as to cover each one wholly or in part. Folds of peritoneum, the _omenta_, connect the stomach with the other viscera, the most important being the _great omentum_, which has one layer descending from the anterior and another from the posterior wall of the stomach. The _mesenteries_ are double layers of peritoneum which hold the intestines to the vertebræ and posterior wall. Between their folds run the blood-vessels.

=Abdominal Regions.=--For convenience of description the abdominal cavity has been divided into nine regions by means of two transverse parallel lines, the one through the ninth costal cartilages and the other just over the iliac crests, and two perpendicular parallel lines through the cartilage of the eighth rib and the middle of Poupart’s ligament on either side. These nine regions have been named as follows: The right and left hypochondriac regions up under the ribs with the epigastrium between, the right and left lumbar regions next below with the umbilical between, and the right and left inguinal with the hypogastric between. Others divide it into quadrants by one line drawn across and another down through the umbilicus. The contents of the abdomen in full are the stomach, intestines, liver, gall-bladder, spleen, pancreas, kidneys, suprarenal capsules, and the great vessels, that is, the organs of digestion and excretion. When distended the bladder extends up into the abdominal cavity, as does the uterus also when enlarged.

=Salivary Digestion.=--Although most of the digestive organs are situated in the abdomen, the food enters the body through the mouth, where its prehension is a voluntary act. Here digestion also begins and from the first the process is a double one, mechanical and chemical, mechanical digestion consisting largely of muscular movements by which the food is ground up and carried through the digestive tract. Thorough mastication or grinding of the food by the teeth is necessary, while the tongue assists by moving the food about and by mixing it thoroughly with the _saliva_, a viscid fluid composed of water and salts and having a slightly alkaline reaction. The saliva is secreted by the parotid, sublingual, and submaxillary glands, and serves to soften and dissolve the food and by virtue of its unorganized ferment, _ptyalin_, to convert starch into sugar. Upon proteins and fats it has practically no digestive action. Moderate warmth and an alkaline medium favor its action, while extremes of heat or cold or an acid medium hinder it. There is little absorption in the mouth, though starch, nicotine, and alcohol may be absorbed in small quantities.

=The Pharynx.=--When the food is ready for deglutition or swallowing, it is thrust back into the pharynx, a somewhat conical, musculo-membranous sac, situated, base upward, behind the nose and mouth and behind, but somewhat above, the larynx. The pharynx is about four and a half inches long and ends on a level with the cricoid cartilage in the esophagus or gullet. It is attached to the vertebræ at the back and opens in front into the mouth. The posterior nares, the Eustachian tubes, and the larynx also open into it, the last being protected by the _epiglottis_, which closes during deglutition to prevent food from entering the air passages, just as the soft palate is drawn back to prevent regurgitation of food into the nose. There are three coats to the pharynx: 1. a mucous coat continuous with that of the mouth and ciliated down to the floor of the nares; 2. a fibrous coat, and 3. a muscular coat containing among others the constrictor muscles which serve to carry the food down to the esophagus. Its arteries are branches of the external carotid and its nerves come from the spinal accessory and the sympathetic. Occasionally a _foreign body_ gets lodged in the pharynx just out of reach of the finger and threatens strangulation. _Retropharyngeal abscess_ on the posterior wall occurs rarely.

=The Esophagus.=--From the pharynx the food passes to the cardiac orifice of the stomach, opposite the tenth dorsal vertebra, through the esophagus, a muscular tube about nine inches long, which collapses when empty, its lumen then appearing as a transverse slit. It, too, has three coats: 1. an inner mucous coat; 2. an areolar coat, and 3. a muscular coat, the muscles being arranged in two sets, an outer longitudinal layer and an inner circular layer. By a series of rhythmic contractions, especially of the circular fibers, the food is pushed along, though sometimes with liquid food there is no peristaltic action of the esophagus, the pharyngeal muscles alone sending it to the stomach. At the lower end of the esophagus an especially strong band of circular muscle fibers form a sort of sphincter, which prevents the regurgitation of food. The whole act of swallowing is a reflex, not a voluntary act and is due to irritation set up by the stimulus of the foreign body, the food. _Stricture of the esophagus_ is common and may be of three kinds: 1. spasmodic, occurring in nervous women; 2. fibrous, due to scar tissue, or 3. malignant, due to cancer.

=The Stomach.=--The stomach is a pear-shaped dilatation of the alimentary canal, lying under the liver and diaphragm in the epigastrium and left hypochondrium and connecting the esophagus with the small intestine. It lies largely behind the ribs, but the greater curvature is only two fingers’ breadth above the umbilicus and can be manipulated through the skin. The _cardiac end_, into which the esophagus enters, is the larger and points upward to the left. The lesser and lower end, known as the _pylorus_, is at the right and its opening into the small intestine is guarded by the _pyloric sphincter_. The lesser curvature is concave and on the upper surface; the greater, convex and on the under surface. The great omentum is attached to the latter.

In _size_ the stomach varies more or less, that of a man generally being larger than that of a woman, but it is usually about ten inches long and four or five inches across. It has a capacity of about five pints and serves as a storehouse for food.

The stomach has four _coats_: 1. a serous coat derived from the peritoneum; 2. a muscular coat of three layers with longitudinal fibers continuous with those of the esophagus, circular fibers, and oblique fibers; 3. an areolar coat, and 4. a mucous coat, which, when the stomach is empty, is thrown into longitudinal folds or _rugæ_, and whose surface is covered with glands, the _gastric glands_, for the secretion of the digestive fluids.

The _arteries_ come from the celiac axis and the _nerves_ from the pneumogastric and the solar plexus.

_Ulcer_ and _cancer_ of the stomach are both rather common. In the former there is apt to be _hyper_-acidity and in the latter _hypo_-acidity, but the rule does not always hold. In cases of ulcer there may be hemorrhage and even perforation. Such hemorrhage can be distinguished from hemorrhage from the lungs by its slightly acid odor and by the frothy character of hemorrhage from the lungs. There is much irritation at the pylorus and where there is irritation there is liable to be cancer.

=Gastric Digestion.=--In the stomach the food is churned and thoroughly mixed with the gastric juices, and it is also subjected to a propulsive movement that drives it on to the intestine. When it comes to the stomach it is semi-solid and when it has become fluid or semi-fluid, in which state it is known as _chyme_, it is ready to pass on. Before it can do so, however, it must overcome the strong pyloric sphincter, and this it does by the muscles about the sphincter pushing it constantly on until the sphincter gives way. Probably most of the propulsive movements take place within a few inches of the pylorus.

The _gastric juice_ is secreted by glands in the wall of the stomach and poured out through little tubules which project from the surface. It is a thin, almost colorless fluid with a sour taste and odor due to the presence of free _hydrochloric acid_, an important element in digestion. Probably when the stomach is empty and for some twenty minutes after the appearance of food there is no hydrochloric acid present and, the food being alkaline, salivary digestion continues. Then, called forth by the presence of the food, the hydrochloric acid appears and salivary digestion ceases in the acid medium. Little digestion of starches or fats takes place, the chief action being on proteins, which are converted into soluble peptones. For besides hydrochloric acid the gastric juice contains two ferments: 1. _pepsin_, which is particularly active in aiding the digestion of proteins, and 2. _rennin_, which especially affects milk. Neither hydrochloric acid nor pepsin seems capable of digesting food alone, but each is essential to the other. They are secreted by different types of cells, secretion depending upon the nerve supply and upon the presence of food. Gastric digestion is favored by minute subdivision of the food and by the right proportion of hydrochloric acid, which should be 0.2 per cent. Body temperature is also advantageous. Except that proteins are put in solution and partly digested, little digestion goes on in the stomach, and though the rugæ afford a large absorbing surface, little absorption takes place, although more takes place than in the mouth and in time most foods, except fats, can be absorbed. The time of digestion varies with different foods and in different people, but probably three to five hours are necessary. The food leaves the stomach as _chyme_, a fluid of about the consistency of pea soup.

_Vomiting_ is more or less the reverse of swallowing and is generally preceded by a feeling of _nausea_, which starts up _retching_, a more or less involuntary effort of the stomach to throw off its contents. To relieve the retching a long breath is taken, followed by a deep expiration that opens the cardiac end of the stomach and allows the abdominal muscles to force the food out. After much vomiting and prolonged retching the pyloric end of the stomach may be affected and bile will then appear in the vomitus. _Artificial vomiting_ may be produced by irritation of the gastric nerve center in the brain or by irritation of the stomach itself.

=Intestinal Canal.=--From the stomach the food passes into the intestinal canal, a convoluted tube which extends from the stomach to the anus and in which, more particularly in the upper portion, the greater part of the digestion and absorption of food takes place. This tube, which is about six times the height of its possessor, consists of two parts, the small and the large intestines, the first four-fifths, or about 25 feet, being small intestine. It occupies the central and lower parts of the abdominal cavity and a small portion of the pelvic cavity, and is attached to the spine by the mesentery, which, however, allows great freedom of motion, so that there is little fixation to the loops of the small intestines.

=The Small Intestine.=--The small intestine opens out of the stomach and has three divisions: 1. the _duodenum_, which is only about ten to twelve inches long; 2. the _jejunum_, so called because it is generally empty after death, which is about two-fifths of the remainder and lies chiefly in the umbilical region and the left iliac fossa, and 3. the _ileum_ or _curved intestine_, the remaining three-fifths, which gets its name from its numerous coils and which lies in the middle and the right side of the abdomen. There is no direct division between the jejunum and the ileum, but the first part of the former and the last part of the latter are quite different in character. At its entrance into the large intestine the ileum is guarded by the _ileo-cecal valve_.

The same _coats_ continue in the small intestine as were found in the stomach, but they are here much thinner and the inner coat is shaggy, like velvet, with innumerable minute processes called _villi_, which greatly increase the absorbing surface. In fact, the great length of the intestine as well as the presence of the villi is aimed to provide a large surface to absorb the food as it passes, an even greater increase of surface being provided by the fact that the intestinal wall is thrown into folds, the _valvulæ conniventes_. Each villus is covered with a layer of columnar epithelial cells and has within connective tissue, in which are found a fine capillary network and open lymph spaces from which leads a single lacteal vessel.

Closely connected with the lymphatic vessels are the _solitary glands_, small round bodies the size of a small pin’s head. _Peyer’s glands_ or _patches_ are patches of solitary glands opposite the mesenteric attachment and are largest and most numerous in the ileum. In typhoid fever they are involved and may become the seat of ulcers. There are also the _glands of Lieberkühn_ which secrete the succus entericus.

The _arteries_ of the small intestine, which include the superior mesenteric, are from the celiac axis and the _nerves_ are from the superior mesenteric plexus of the sympathetic. The _veins_ empty chiefly into the portal system.

The _movements_ of the intestine, like those of the esophagus, are peristaltic, but the action is complicated by the fact that the tube is not straight but in coils.

=Intestinal Digestion.=--The food, which enters the duodenum as chyme, there comes in contact with the bile and the pancreatic juice, which together but unmixed enter the duodenum from their respective ducts by a common orifice. As in the stomach, the digestive juices are called forth by the presence of food. The _bile_ is secreted in the liver, from which it flows away through the hepatic duct, which joins the cystic duct from the gall-bladder to form the common bile duct. Through this it flows into the intestine during digestion, but between whiles it passes up into the gall-bladder, where it is stored for future use and whence it is expelled when needed. When pure it is a thick, viscid liquid, varying from a bright red to a greenish-yellow in color according to the pigments present, and of an alkaline reaction. It consists chiefly of the bile pigments, _biliverdin_, which gives the green color, and _bilirubin_, which gives the red color, and of bile salts in solution, _cholesterin_, which probably forms the basis of many gall stones, is also present. Bile is a disinfectant to the bowel and a lubricant for the feces. How much digestive action it has is a question, but it affords the necessary alkaline medium for the pancreatic juice to act in.

The _pancreatic juice_ is secreted by the pancreas, from which it enters the intestine through the pancreatic duct, and is probably the most important fluid in the digestive process. It is clear, practically colorless, slightly viscid or gelatinous, and quite strongly alkaline in reaction, owing to the presence of sodium carbonate. It contains three ferments, _amylopsin_ for the digestion of starch, _trypsin_ for the digestion of proteins, and _steapsin_ for the digestion of fats. By it, as by the saliva, starch is turned into sugar or maltose, in which form it is absorbed, while proteins are converted into peptones, as they are in the stomach. Since, however, fats are acted on nowhere else, the chief function of the pancreatic juice may be considered to be the digestion of fats. Having broken through their albuminous envelope, it divides them into glycerine and fatty acids and then emulsifies them with the assistance of the bile.

The food also comes in contact with the _succus entericus_, a juice secreted by the glands of Lieberkühn in the small intestine, whose chief action is the conversion of sugar into glucose.

=Absorption.=--As the food is absorbed from the intestine it is liquid and entirely digested and is known as _chyle_. Practically all absorption takes place from the small intestine, though there is a little in the large intestine. It takes place in two ways: 1. through the portal vessels and 2. through the _lacteals_, which are the lymphatic vessels of the small intestine. Fats are absorbed practically entirely by the lacteals. They enter the cells covering the villi, travel thence to the lymph spaces, and so into the lacteal or main lymph channel, whence they are carried to the thoracic duct and the general circulation. From the blood they are absorbed as fat and stored up as adipose or fatty tissue, which is found throughout the body in connective tissue about the organs. Organic salts and water are for the most part absorbed by the portal system, which they reach through the capillaries of the villi and through which they go to the liver. Starches, in the form of sugar, pass between the cells of the villi into the lymph spaces, from which they are taken up by the capillaries. On the way to the liver maltose becomes dextrose. Proteins, in the form of peptones, pass through the layer of epithelial cells to the lymph spaces and then to the capillaries, an active part being taken by the cells. By the time they reach the liver the peptones have been changed back into proteins. In fact, peptones seem to have some poisonous effect upon the blood if they get into it as such.

=The Large Intestine.=--The large intestine differs from the small in size and in fixity of position, lying curved in horseshoe shape above and around the small intestine. It is five or six feet long, large in caliber, and is thrown into crosswise folds. It has the same four _coats_ as the small intestine, but the mucous coat is pale and smooth, without villi. Its _glands_ are the crypts of Lieberkühn and the solitary glands. The _arteries_ are branches of the superior and inferior mesenteric and the _nerves_ come from sympathetic plexuses.

The blind sac lying in the right iliac fossa, with which the large intestine begins, is called the _cecum_, and into this the ileum opens, the ileo-cecal valve preventing regurgitation. Just below the ileo-cecal opening is the _vermiform appendix_, a narrow, worm-like tube with a blind end, varying in length from one to nine inches, but generally about four and one-half inches long, which, so far as is known, is functionless as well as dangerous. People have been born without an appendix and it has in rare instances grown again after operation. Its base is located in the living by _McBurney’s point_, a point two inches from the anterior superior spine of the ilium on a line drawn from the spine to the umbilicus.

From the cecum the intestine ascends in what is known as the _ascending colon_ along the abdominal wall at the right to the under surface of the liver, where it turns in the _hepatic flexure_ abruptly across the body to the left, passing below the liver, stomach, and spleen in the _transverse colon_. In the _splenic flexure_ it turns down the left abdominal wall, the _descending colon_ passing to the crest of the ilium, where there is another curve, the _sigmoid flexure_, leading to the _rectum_, which passes for six or eight inches down along the vertebræ, a little to the left, to the _anus_, the external opening. This opening is guarded by two _sphincter muscles_, about an inch apart, the internal and external sphincters. The coils of the small intestine lie below the transverse colon, covered mostly by the omentum. The splenic flexure is behind the stomach and below the spleen and is slightly higher than the hepatic flexure. The sigmoid flexure can be felt in the left inguinal region in thin people.

The fact that the _rectum_ is somewhat to the left is of importance in childbirth because if the rectum is packed, it may turn the child’s head in the wrong direction.

No digestion goes on in the large intestine, the function being to dry by absorbing water. The _movements_ are practically the same as those of the small intestine except that they are much less active. Fermentation makes the contents acid. By the time food reaches the rectum it has been thoroughly digested and has given up its nourishment. It is then expelled as waste matter or _feces_. _Defecation_ combines the involuntary movements of peristalsis and relaxation of the sphincters with the voluntary aid of the abdominal muscles. The _ano-spinal reflex_, by which movements of the bowel are regulated, is in the lumbar enlargement of the cord.

The _hemorrhoidal veins_ in the lower rectum are connected with both the systemic and the portal veins and have no valves so that, as they are subjected to much strain, they often become varicose and dilated. This condition is called _hemorrhoids_ or _piles_. _Obstruction_ of the intestine may be caused by the growth of a constricting band, by _intussusception_ or telescoping of the intestine on itself, especially at the ileo-cecal valve, or by _volvulus_ or twisting. _Foreign bodies_ are sometimes found in the appendix but they are not usually the cause of appendicitis. _Cancer of the intestine_ is common and its mass is apt to cause obstruction with all its attendant symptoms. It may necessitate an artificial anus. _Hernia_ or _rupture_ may also occur and the hernia may become strangulated.

=Food and Metabolism.=--Anything serves as food that replaces or hinders the loss to which the component parts of the body are liable. Proteins, carbohydrates, fats, some mineral matters, as salt and perhaps iron, and water are needed. The energy once expended by plants or animals in the formation of the materials which serve as food is set free in the body by the breaking up of these complex substances into their original elements, which are then recombined into the complex materials needed for the body’s life and growth. This process of building up complex materials from simple ones is known as _anabolism_ and that of breaking them down as _katabolism_, while the two combined form the complete cycle of _metabolism_. Those foods have the best value that give up their energy most readily. For their combustion, heat, oxygen, and water are needed. Hunger indicates that the supply of material for katabolism has been used up and that more is needed, just as thirst indicates the need of the system for more fluids.

The proteins or nitrogenous foods include all animal foods except fats, fish, crustaceans, eggs, milk and its products, certain vegetables, especially the lentils, that is, peas and beans, and gelatine. The fats include various fats and oils commonly eaten. The carbohydrates are the starchy foods, as cereals, sugars, fruits, and most vegetables, in fact, practically all except the lentils. Various beverages and condiments have no great nutritive value but serve to stimulate the appetite and to excite the secretion of the digestive juices. Coffee, tea, and alcohol are stimulants.

The different classes of foods have different functions in the nourishment of the body. The proteins are primarily tissue-builders and also help somewhat in force production. The fats are essentially heat-producers, though they too help in force production. The carbohydrates are chiefly important as force-producers, though they also produce heat and to a certain extent save protein oxidation. Fat is formed by all three but only in small amount by proteins. So no one food can form the whole diet but there must be variety. Carbohydrates and fats are not sufficient for life, some protein is necessary. Carbohydrates are more digestible than fats but have less potential energy. Gelatine saves waste of nitrogen, though it does not increase the supply. Water and salts are not nutritive but they aid the body processes, the water helping to dilute and dissolve substances for digestion.

The end-product of the consumption of protein is _urea_, which is eliminated by the kidneys. Just where it is formed is unknown, but many think in the liver. A trifling amount of urea is also eliminated in the sweat and in the breath as well as in the feces. Proteins increase nitrogenous metabolism and also the metabolism of other foods, but the amount of nitrogen eliminated is just equal to that taken in. Probably some comes from the tissues themselves and not from the food. The oxidation of carbohydrates and fats is measured by the amount of carbon excreted. At first as much is given off as is taken in, but after a while the carbohydrate is stored up as glycogen in the liver and the fats are stored as fat.

The amount of food needed varies with the person’s size and occupation, less being needed for a child than for an adult and more for a hard-working man than for one who is doing less work. In general, 100 to 130 grams of protein, 40 to 80 grams of fat, 450 to 550 grams of carbohydrates, 30 grams of salts, and 28,000 grams of water is a fair amount.

Foods are cooked to make them more digestible and to develop their flavor, so that they will taste better. Cooking also kills germs and parasites that might be harmful. Meats should be cooked rapidly on the outside to coagulate the surface albumen and keep in the juices. The heat, besides coagulating the albumen, turns the tough parts to gelatine. In cereals the tough envelope of cellulose is broken up and in vegetables the tough fibrous parts are softened and made more digestible.

=The Liver.=--Below the diaphragm on the right and extending across above the stomach, resting in a way upon the transverse colon and the small intestine, is the liver, the largest gland in the body. It is dark reddish-brown in color and is larger in proportion in the child than in the adult. The upper surface is convex and lies in contact with the diaphragm, while the lower surface is concave to fit over the organs beneath. With a full breath it comes downward and forward, with the edge against the abdominal wall, and can be easily felt. Numerous strong ligaments, including the suspensory ligament from the diaphragm, hold it in place, and it is more firmly fixed than any other of the abdominal organs, probably on account of its large size. It is divided by fissures into five _lobes_, of which the most important are the right and left, the right one being the largest and containing the gall-bladder in one of its fissures.

The liver tissue contains a large number of _cells_ collected into _lobules_, in the center of each of which is a blood-vessel, the _intralobular vein_, from which a network of capillaries extends to the edge of the lobule, there being a capillary on either side of each row of cells. Between the cells also are the _intercellular biliary passages_, roots of the bile ducts which exist in the connective tissue between the lobules and which join to form two main ducts, one from the right and the other from the left lobe. By the union of these two ducts the _hepatic duct_ is formed, which, after a course of one or two inches, joins the cystic duct from the gall-bladder to form the _ductus communis_ or _common bile duct_.

The liver has a double _blood supply_, the _hepatic artery_ from the celiac axis bringing nourishment to the connective tissue and the walls of the blood-vessels, while the capillaries between the cells come from the _portal vein_, which, being formed by the junction of the superior and inferior mesenteric, the splenic and the gastric veins, contains the proteins and carbohydrates absorbed during digestion. After its passage through the liver this blood from the portal vein is collected once more into the hepatic veins, which convey it to the inferior vena cava. During its passage, however, various changes take place, for the liver plays an important part in the metabolic processes of the body.

The liver has two principal _functions_, the secreting of bile and the storing up of glycogen. The secretion of _bile_, which is a very important aid to digestion, is probably a reflex act, the presence of peptones in the portal blood after meals acting as a stimulant to the liver cells. For food at once increases the secretion of bile, which is poured from the cells into the small bile ducts and finally passes into the hepatic duct and so to the gall-bladder, where it is stored until needed. Although the flow from the liver is constant, the amount secreted reaches its maximum when the food gets down into the small intestine, that is, four or five hours after eating, there being a lull before that. Apart from the process of secretion, the manufacture of the bile pigments, _bilirubin_ and _biliverdin_, which are made from the hemoglobin of the blood, seems to require some special action on the part of the liver cells.

The _glycogen_, which is manufactured and stored in the liver cells, is a clear hyaline substance, akin to starch and capable of being converted into sugar by the starch ferment. Probably there is some such ferment in the blood which converts the glycogen into sugar as soon as it passes from the liver into the blood, though what it is, is not known. Neither is it known just how glycogen is formed, but it is manufactured chiefly after a mixed meal in which carbohydrates predominate, proteins having little and fats no effect upon its formation. It is undoubtedly formed from the sugar in the portal blood and the process requires some work on the part of the liver cell itself. Probably there is always some sugar in the circulating blood which, as it is used up, must be made good. If there it not enough in the diet, the liver supplies the deficiency from its store of glycogen.

Glycogen is found also in the muscles, in the placenta as food for the fetus, in leucocytes, and to a slight extent in cartilage. In fact, it is the form in which carbohydrate material is supplied to the tissues as needed. Normally, much of the sugar is used up by the blood and its cells in metabolism, giving rise to heat and energy. In muscles glycogen is probably digested as lactic acid, as before action muscle is neutral or slightly alkaline and after action acid.

When the liver is deranged and allows the glycogen to pass out into the blood too freely, or when the glycogen is not held as such but turned to sugar and passed out in large quantities, _sugar in the urine_ or _diabetes mellitus_ results.

Besides its secreting function the liver has an _eliminative function_ and plays an important part in purifying the blood, removing from it many poisonous and narcotic substances. It is thought by some, though it has not been proved, that _urea_, the end-product of protein metabolism, which is brought by the blood to the kidneys and there excreted, is formed in the liver. At any rate, urea is formed not only from the nitrogenous food eaten but from the metabolism of protein substances in the tissues, being purely a waste product, from which the nutritious substances have been absorbed. The amount thrown off is an accurate gauge of the amount of protein metabolism going on. The process of its manufacture is doubtless very complex.

_Ptosis_ or _dropping_ of the liver sometimes occurs and is due to the stretching of the ligaments. _Rupture_ is common, generally as the result of a fall from a height, on account of its size and friability. The liver is also subject to many diseases. _Cirrhosis_ occurs in people who drink a good deal and in its later stages is accompanied by _ascites_, an accumulation of fluid in the abdominal cavity. When there is a general accumulation of fluid throughout the body it is known as _anasarca_. _Syphilis_ causes enlargement of the liver. _Abscesses_ occur, perhaps oftener in the tropics than farther north, and may break into the lungs, stomach, or intestine.

=The Gall-bladder.=--The gall-bladder, which is simply a reservoir for the bile, is a pear-shaped organ three inches long and one inch broad. It lies in a fossa on the under side of the liver, with the large end or fundus touching the abdominal wall just below the ninth costal cartilage. Here it can be felt as a small mass in empyema of the gall-bladder. Normally it holds a little over one ounce, but with occlusion it may become stretched. Its duct is the _cystic duct_, which joins the hepatic duct in the common bile duct, but bile only passes up into the gall-bladder when the opening into the duodenum is closed, that is, between meals.

If one of the bile ducts is stopped up by a stone or cancer or for any other cause, the bile backs up in the liver, the pigments are absorbed into the circulation, and _jaundice_ results. In this condition operation is dangerous, as the time of coagulation of the blood, normally five minutes or less, is much delayed. _Gall stones_, formed largely of bile pigments and cholesterin, sometimes collect in the gall-bladder, where they cause irritation and may give rise to _empyema_ of the gall-bladder. The stones vary in size from a pea to a hen’s egg and when small may be very numerous.

=The Pancreas.=--Another accessory organ of digestion is the pancreas, the _abdominal salivary gland_, as it is sometimes called on account of its close resemblance to the parotid gland. This is a grayish-white racemose gland, six and a half inches long by one and a half inches wide and one inch thick, lying behind the stomach on a level with the first and second lumbar vertebræ and shaped like a pistol with its handle toward the right. In an emaciated person it can be felt. The _pancreatic duct_ runs the whole length of the gland from left to right and conveys the _pancreatic juice_ from various little glands in the substance of the organ to the duodenum, into which it empties along with the common bile duct by a common orifice. The _arteries_ are from the celiac axis and superior mesenteric, the _veins_ belong to the portal system, and the _nerves_ come from the solar plexus.

Surgically the pancreas is of no special importance, though _acute pancreatitis_ does occasionally occur and is a very serious condition and one hard to diagnose.

=The Spleen.=--The largest and most important of the ductless glands is the spleen, an oblong, flattened organ lying deep in the left hypochondriac region between the stomach and diaphragm above the descending colon, and corresponding to the ninth, tenth, and eleventh ribs. It is soft, brittle, and very vascular. Its _artery_ is a branch of the celiac axis and the _vein_ belongs to the portal system. Its _nerves_ are the pneumogastric and branches from the solar plexus. The _function_ is not well understood but probably it is connected with or related to the vascular system in some way. Perhaps it manufactures blood corpuscles.

The spleen varies more in size than any other organ. Normally it cannot be felt, but in typhoid it usually can. It is generally atrophied in old age and hypertrophied in almost all acute infectious diseases, especially in typhoid fever and malaria. In leukemia it is often greatly enlarged. Sometimes in violent falls it is _ruptured_ and there is considerable hemorrhage.

=The Suprarenal Capsules.=--The other ductless glands, the suprarenal capsules, yellowish triangular bodies, are situated just above and in front of the kidneys. Their function is important but not well understood. Death, accompanied by great muscular weakness, follows the removal of both, and when they are diseased, similar weakness is observed and the skin becomes bronzed. Injection of the extract of the suprarenals stimulates the muscular system. So probably they secrete into the blood minute quantities of a substance or substances beneficial to the body, especially to the muscular system.

=The Kidneys.=--The two kidneys lie on either side of the vertebræ at the back of the abdominal cavity and behind the peritoneum, between the last dorsal and the third lumbar vertebræ, their inner edge being about one inch from the spinous processes. They are bean-shaped, four inches long, two inches wide, and one inch thick, and are embedded in a mass of fat and loose areolar tissue. They can be felt only when misplaced or when enlarged, as by tuberculosis or malignant disease.

The whole kidney is enveloped in a fibrous _capsule_ which normally may be peeled off but which in some diseases becomes adherent. On the internal border is a _fissure_ or _hilum_, through which pass the blood-vessels and the ureter. Upon entering, the ureter dilates into a sac, the _pelvis of the kidney_, into which project the _Malpighian pyramids_ of the _medullary substance_, a substance made up of the straight uriniferous tubules and blood-vessels. Outside the medullary substance and just under the capsule is the _cortex_, containing the _Malpighian bodies_, blood-vessels, and the _convoluted tubules_ or _loops of Henle_. Each Malpighian body contains within a capsule a plexus of capillaries, the _glomerulus_, with an afferent arteriole and an efferent vein. The _renal artery_ is a branch of the aorta and the _nerves_ are from the solar plexus.

_The Urine._--As the blood passes through the glomeruli, the urine is filtered off as it were, probably by a process of transudation rather than simple filtration. The cells lining the tubules also play an important part in its formation, not by secreting new substances but by taking up those brought by the blood and discharging them into the convoluted tubules, from which the urine passes through the straight tubules of the medulla to the pelvis, to be carried thence by the ureter. The process of the formation of the urine, therefore, is not purely a process of secretion but requires some action on the part of the kidney, though no new substances are secreted in the kidney.

The passage of the urine down through the ureters is assisted by a kind of peristaltic action in the walls of the ureters and it is expelled from the body by the act of _micturition_, which is mostly voluntary, though a certain amount of nervous mechanism controls it. The seat of this nervous mechanism is in the lumbar enlargement of the spinal cord. In some nervous conditions, especially where there is injury to the spinal cord, there is _involuntary micturition_.

The urine is a watery solution containing many waste products, especially urea. It is generally amber in color, varying in shade with circumstances, with an aromatic, characteristic odor when fresh. It is acid in reaction and has a specific gravity of about 1020, though this too varies with circumstances. Besides water, which is its chief constituent, it contains urea, uric acid, organic acids, urates, inorganic salts, including sodium chloride and phosphates of calcium and magnesium, a certain amount of ammonia, and certain pigments. Its acidity is due to acid sodium phosphate in solution but varies with the food, and in disease the urine may become alkaline when passed. After standing a few hours in a warm place it decomposes and becomes alkaline.

The quantity, which is normally three pints or fifteen hundred cubic centimeters in twenty-four hours, varies with the amount of fluid drunk, the amount of perspiration, etc. The amount secreted depends chiefly, however, upon the flow of the blood through the kidneys; the greater the flow of blood, the larger the amount of urine formed; and the blood flow is determined by blood pressure and by vasomotor action. Secretion also seems to be increased by the presence of urea, which apparently serves as a stimulant to the kidney cells.

The excretion of waste materials takes place by three main channels, the lungs, skin, and kidneys, and the materials are of four kinds, _urea_, _carbon dioxide_, _salts_, and _water_. The lungs carry off carbon dioxide and water chiefly, the skin these and inorganic salts, while the kidneys eliminate practically all the urea as well as inorganic salts and water. When the kidneys are not working the skin carries off much urea. In fact, a close relationship exists between the kidneys and the skin in the matter of excretion. Thus, with increased perspiration in warm weather comes decreased urine, while in cold weather the blood is sent in and the urine increased in amount.

To incite action of the kidneys drugs known as _diuretics_ may be used. These act in two ways, by stimulating the kidney cells directly and by acting on the general circulation or nervous system. Any emotional or nervous excitement increases the flow of urine.

There are certain abnormal constituents of urine, of which the two most important are _albumen_ and _sugar_. The former is found only when there is some disturbance of the kidneys, ureters, or bladder, and its presence usually denotes some change in the cells lining the urinary tract. It may occur in congestion of the kidney as well as in disease. Sugar is found only in _diabetes_, the amount varying with the severity of the disease. In _jaundice_ certain bile pigments are present in the urine, giving it a dark brown color and to the foam a greenish-yellow color. Even normal urine has some sediment upon standing, consisting of cells from the urinary tract and mucus. In very acid urine after standing a heavy sediment, whitish or pinkish, _i.e._, brick dust, in color, is thrown down. It does not necessarily denote disease, but shows the urine is acid and concentrated. In _alkaline urine_ there is a sediment due to phosphates.

_Rupture_ of the kidney occurs but is not so serious as rupture of the liver or spleen because the kidney is situated outside of the peritoneum. It necessitates the removal of the kidney, however, and when for any reason one kidney is removed the other increases in size and does double work to compensate for the loss. Removal of both kidneys means death. Sometimes the kidney becomes loose and moves about, a condition known as _floating kidney_. _Perinephritic abscess_ is abscess in the loose fatty tissue about the kidney.

=The Ureters=, one for each kidney, are tubes the size of a goose quill and about fourteen inches long, extending from the hilum of the kidney to the base of the bladder. They have three _coats_, an internal mucous, a muscular, and an external fibrous coat, this last being continuous with the cortex of the kidney and the fibrous tissue of the bladder. In the female the ureters may be felt through the wall of the vagina as they come into the bladder. In tubercular disease of one kidney the ureter becomes inflamed and enlarged and through the vagina feels almost like a lead pencil, a sure diagnostic sign.

=The Bladder and Urethra.=--In their course to the bladder the ureters pass from the abdominal into the pelvic cavity, but before describing the pelvis itself it will be well to complete the account of the urinary organs by considering the bladder and urethra. The _bladder_ is the reservoir for the urine and has muscular walls lined with mucous membrane. A peritoneal coat covers the upper surface and is reflected to the walls of the abdomen and pelvis. It is situated back of the os pubis, the front bone of the pelvis, with its base or fundus directed downward and backward. Normally it is in the pelvis, but when much distended it mounds up into the abdominal cavity, where it can be felt in front as a tumor. It rests on the rectum in the male and on the cervix in the female and is held in place by numerous ligaments. When empty it may be Y-shaped, but it becomes oval when distended. Its capacity is about one pint.

The lower abdominal wall and the anterior wall of the bladder may be wanting congenitally. In paralysis of the sphincter at the neck of the bladder distention results. _Stones_ may be found in the bladder.

From the neck of the bladder the urine passes out of the body through the _urethra_. This in the male passes down through the penis and is about ten inches long. Except when urine is passing it is a transverse slit with the upper and under surfaces in contact, while at the end of the penis the slit of the meatus urinarius is vertical. When the penis is flaccid, the urethra describes a sharp curve before its entrance into the bladder, but it becomes approximately straight when the penis is raised at right angles to the body--an important point to remember in catheterization.

In the female the urethra is straight and much shorter, being only about one and a half inches long. The _meatus urinarius_ is in the anterior vaginal wall about one inch behind the clitoris.

Sometimes the urethra is _ruptured_ in a fall. _Stricture_ of the urethra occurs sometimes after gonorrhoea, owing to the formation of scar tissue following ulcer.