436 DIGESTION. 



the saliva must be absorbed and pass into the blood, and it must in this 

 way go through an intermediate circulation in the organism. Thus the 

 organism possesses in the saliva an active medium by which a constant 

 stream, conveying the dissolved and finely divided bodies, passes into 

 the blood from the intestinal canal during digestion. The relation of 

 the saliva or the salivary glands to the secretion of gastric juice will be 

 mentioned in the next section. 



Salivary Concrements. The so-called tartar is yellow, gray, yellowish-gray, 

 brown or black, and has a stratified structure. It may contain more than 200 

 p. m. organic substances, which consist of mucin, epithelium, and LEPTOTHRIX- 

 CHAINS. The chief part of the inorganic constituents consists of calcium car- 

 bonate and phosphate. The salivary calculi may vary in size from that of a 

 small grain to that of a pea or still larger (a salivary calculus has been found 

 weighing 18.6 grams), and they contain variable quantities of organic substances 

 (50-380 p. m.), which remain on extracting the calculus with hydrochloric acid. 

 The chief inorganic constituent is calcium carbonate. 



II. THE GLANDS OF THE MUCOUS MEMBRANE OF THE STOMACH, AND THE 



GASTRIC JUICE. 



The glands of the mucous coat of the stomach have long been 

 divided into two distinct classes. Those which occur in the greatest 

 abundance and which have the greatest size in the fundus are called 

 fundus, rennin or pepsin glands, and the others, which occur only in 

 the neighborhood of the pylorus, have received the name of pyloric 

 glands, sometimes also, though incorrectly, called mucous glands. The 

 division of these two forms of glands in the mucous membrane of the 

 stomach is essentially different in various animals. The mucous coating 

 of the stomach is covered throughout with a layer of columnar epithelium, 

 which is generally considered as consisting of goblet cells that produce 

 mucus by a metamorphosis of the protoplasm. 



The fundus glands contain two kinds of cells: ADELOMORPHIC qfchief 

 cells, and DELOMORPHIC or COVER cells, the latter formerly called 

 RENNIN or pepsin cells. Both kinds consist of protoplasm rich in pro- 

 teins; but their relation to coloring-matters seems to show that the 

 protein substances of both are not identical. The nucleus must con- 

 sist chiefly of nuclein. Besides the above-mentioned constituents, the 

 fundus glands contain as more specific constituents several enzymes 

 or their zymogens, besides a little fat and cholesterin. 



The pyloric glands contain cells which are generally considered as 

 related to the above-mentioned chief cells of the fundus glands. As 

 these glands were formerly thought to contain a larger quantity of mucin, 

 they were also called mucous glands. According to HEIDENHAIN, inde- 

 pendent of the columnar epithelium of the excretory ducts they take no 

 part worthy of mention in the formation of mucus, which according to 



