154 MANUAL OF PHYSIOLOGY. 



more easily, and have darker granules than the central cells. 

 On account of their position they have been called " parietal," 

 " marginal or border cells " (Belegzellen), 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 ana- 

 tomical differences denote differences of function. 



THE 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 vari- 

 able, and depends upon the amount and character of the food ; in 

 well-fed dogs it has been estimated to be one-tenth of the body 

 weight. 



1. It contains, in man, about .2 per cent, of free hydrochloric 



acid, 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, 



