'266 DIGESTION 



milk and bread with the same N-content (about 3.4 g.), there appeared in the 

 isolated sac 27, 34 and 42 c.c. respectively of gastric juice having- a digestive 

 power of 4.0, 3.1 and 6.16 mm. of egg albumin (cf. page 245). Since the di- 

 gestive power is proportional to the square root of the quantities of pepsin, the 

 quantities in this series would be to each other as 430, 340, and 1,600. 



The center of these reflexes mediated by the vagus probably coincides with 

 the vagus nucleus. The psychic influence on the secretion is exercised natu- 

 rally through the cerebrum. In the dog Bechterew obtained a secretion of 

 gastric juice and of gastric mucus on stimulating a region lateral to the 

 anterior portion of the gyms sigmoides just at the forward end of the third 

 convolution. Stimulating for four to five minutes the secretion continued 

 for thirty to fifty minutes and exhibited an unmistakable similarity with that 

 obtained by fictitious feeding. After extirpation of this cortical field no 

 secretion appeared on offering food. 



The mechanism of the secretion which is independent of the vagus is much 

 more difficult to explain. It might be caused either by some reflex process or 

 by the direct exciting effects of absorbed substances upon the glands themselves. 

 There are difficulties in the way of both hypotheses and the matter cannot be 

 regarded as settled. 



B. THE GASTRIC GLANDS 



The mucous membrane of the stomach presents considerable differences be- 

 tween the fundic and pyloric portions. The pyloric portion is pale and whitish 

 in color and is beset by a few high folds, here and there united together. The 

 rest of the mucous membrane has a reddish-yellow or reddish-gray color, and 

 possesses numerous folds bound together into an irregular network, and in addi- 

 tion to these, fine secondary folds likewise arranged as a net. Into the depres- 

 sions formed by the folds open the gastric glands, whose epithelial cells are 

 continuous with the epithelium which clothes the free surface of the mem- 

 brane. 



This superficial epithelium secretes the gastric mucus and behaves prob- 

 ably like similar cells of the salivary glands. 



The glands of the mucous membrane are tubular and belong to two dif- 

 ferent types, one constructed of one kind of cells, the other of two kinds. 

 The spatial distribution of the two kinds presents certain differences in dif- 

 ferent mammals. In the dog and man the glands formed of one kind of 

 cells occur only in the pylorus ; those with two kinds occur only in the fundus. 

 For this reason they are named pyloric and fundic glands respectively. The 

 boundary between the two divisions of the mucous membrane is not however 

 very sharp. 



The secreting elements of the pyloric glands are cylindrical cells arranged 

 in a single layer upon the basement membrane of the glands. The fundic 

 glands contain similar cylindrical cells similarly arranged. These cells were 

 discovered by Rollet and Heidenhain, and are called the chief or adelomor- 

 phous cells. 



