are found in the deeper part of the gland tubes. Much the more numerous are small, pale, spheroidal cells, which occupy the lumen of the gland and form the regular cell lining of its cavity. These cells have been called the "chief cells" (Hauptzellen), "central" or spheroidal cells.

The cells of the other form are comparatively few, being altogether wanting in some of the glands. They are larger and more striking than the central or spheroidal cells between which

Diagram showing the relation of the ultimate twigs of the blood vessels (V and A), and of the them, viz., above cylindrical cells; small, pale cells in the lumen, outside of which are the dark ovoid cells.

and the basement membrane they lie scattered here and there over the fundus of the gland, making the delicate membrane bulge. They stain more easily, and have darker granules than the central cells. On account of their position they have been parietal," "marginal or border cells" (Belegzellen),

called "

and from their oval shape, which equally well distinguishes them from the other, "ovoid cells." (See Fig. 69.)

There is a different class of glands, the so-called mucous, found chiefly near the pyloric end of the stomach, in which there is but one kind of cell throughout, and this seems to differ in character from both the varieties in the other glands, resembling rather the cylindrical epithelium covering the surface of the stomach and dipping into the conical orifices which lead to the glands.

The difference between the two kinds of glands found in the stomach, both as regards their distribution and way of branching, and the cells which line the deeper parts of the tubes, is found to vary in different animals. The difficulty of obtaining fresh specimens of the human stomach makes it still uncertain whether the same differences exist in the human subject. The varieties of opinion and drawings published suggest that various stages of gradation from one kind of gland to another are met with in the stomach of even the same animal.

Experimental research does not show decisively that the anatomical differences denote differences of function.

CHARACTERS OF GASTRIC JUICE.

The gastric juice is a clear, colorless fluid with strongly acid reaction. It contains .5 per cent. of solids, its specific gravity being 1002. The amount secreted in the day is extremely variable, and depends upon the quantity and character of the food; in well-fed dogs it has been estimated to be one-tenth of the body weight.

It contains:

1. About .2 per cent. of free hydrochloric acid in man, but

in the dog considerably more. The lactic, formic, butyric, and other acids which have been found in the gastric juice probably depend on the decomposition of some of the ingesta.

2. Pepsin, the specific substance which gives the gastric juice its digestive qualities, is a nitrogenous ferment which, with the foregoing acid, acts on proteids. About .3 per cent. is present in the secretion of the human stomach.

3. Associated with the pepsin are other less-known ferments, one of which curdles milk without the presence of any acid.

4. A variable quantity of mucus is found in the secretion of the stomach.

5. It contains .2 per cent. of inorganic salts, chiefly chlorides of sodium, potassium and calcium.

Method of Obtaining Gastric Secretion.-Formerly, attempts were made to obtain gastric juice by inducing a dog, while fasting, to swallow a sponge, and withdrawing it when saturated with the gastric secretion; or a fasting dog, allowed to swallow insoluble materials, was killed, and the secretion collected from the stomach.

It is best obtained directly from a fistulous opening in the abdominal wall communicating with the stomach. A gastric fistula was first made accidentally in a man by injury. A case in which the surgical treatment of a gunshot wound of the stomach left a permanent fistula, allowed the gastric secretion to be carefully investigated, and proved a valuable subject for experimental research.

It is not a difficult matter to reach the stomach by making an artificial opening through the wall of the abdomen, and, having brought the serous surface of the gastric wall into firm connection with the serous lining of the abdominal wall, to open the stomach. The juxtaposition of the parts, as well as the patency of the fistula, can be secured by a suitable flanged cannula closed with a well-fitting cork. By removing the cork the gastric juice may be obtained in small quantities, and various kinds of food may be introduced through the cannula, and the changes occurring in them studied.

For experimental purposes an artificial gastric juice may be used. This can be made from the gastric mucous membrane of a dead animal (pig) by extracting the pepsin from the finelydivided glandular membrane, with a weak acid (less than .2 per cent.) or, better, with a large quantity of glycerine, and subsequently adding HCl to the extent of .2 per cent.

MODE OF SECRETION.

The gastric juice is not secreted in large quantity when the stomach is empty, but only when the mucous membrane is irritated with some chemical or mechanical stimulus. The swallowing of alkaline saliva acts as a gentle stimulus and causes secretion, so that the surface of the stomach becomes acid. When the lining membrane of the stomach is mechanically stimulated through a fistula it becomes red, and drops of secretion appear at the point of stimulation, but the amount of secretion thus produced is very scanty when compared with that called forth. by chemical irritants.

Thus, ether, alcohol and pungent condiments produce copious secretion. Weak alkaline solutions also cause secretion, but the most perfect form of stimulant seems to be a mass of food saturated with alkaline saliva.

In all probability the secretion of the gastric juice is under the control of a special nerve mechanism, and the way in which the state of activity follows stimulation of the part seems to point to its being a simple reflex act. However, the nervous connections (vagi and splanchnics) between the stomach and central nervous system may all be severed without any marked effect on the secretion, other than that which would naturally follow the changes in the amount of blood supply, which, of course, is greatly altered by cutting the vasomotor nerves- the splanchnics. Whether this be so or not, there must be some connection with the nerve centres, for sudden emotions check the secretions, and the sensations caused by the sight or smell of food give rise to gastric secretion.

It has been suggested that Meissner's submucous ganglionic network may act as a reflex centre and regulate the secretion. But as the reflection from local ganglionic centres has not yet been definitely demonstrated, we are hardly entitled to assume that it occurs here, and since the stimulus comes into close contiguity with the secreting cells, it seems quite as probable that these elements are excited to activity by direct stimulation of their protoplasm.

As in the salivary glands, so in the gastric tubes, the cells

show some structural changes which accompany with great regularity their periods of rest and activity, and therefore may be concluded to be the indications of the internal processes belonging to the production of the specific materials of the secretion.

It appears probable that the chief secretory activity resides in the small central cells, and not in the large ovoid border cells, since no distinct changes can be seen in the latter, and the smaller gland cells seem to contain the pepsin; for if the mucous membrane be treated with weak hydrochloric acid, these central gland cells are rapidly dissolved by a process of digestion, while the border cells simply swell up and become more transparent. So that the outer ovoid cells have no title to their former name of "peptic cells."

The central cells of the gastric glands are finely granular, pale, protoplasmic masses, and continue so during the time when the stomach is empty and the glands not secreting. In the earlier stages of digestion these cells swell up and become turbid and coarsely granular, and stain more readily with the aniline dyes. As the digestive process goes on the cells again diminish in size, but are found to contain a large quantity of peculiar granules, which are discharged from the cell before its return to the ordinary state of rest. The cells are said to be rich in pepsin in proportion to their size; when swollen during active digestion they contain much pepsin, when small, during hunger, they contain but little.

It would therefore appear that the pepsin of the gastric juice. is produced as a distinct and new manufacture by the central cells of the peptic glands, and not by the other cells. Structural changes have also been followed out in the so-called mucous glands and in glands without any of the ovoid border cells, which, taken with the fact that the alkaline secretion of the pyloric end of the stomach, where the mucous glands abound, is capable of rapidly digesting proteid if acid be added to it, tends to show that in these so-called mucous glands pepsin is also produced.

The acid is found chiefly on the surface of the stomach. The mode of its production seems distinct from that of pepsin, but is