DIGESTION. 171 



found that after division of the nerve, secretion was arrested, and that stim- 

 ulation of the peripheral ends with induced electric currents at the rate of one 

 or two per second, caused after a latent period of several minutes' duration 

 a flow of gastric juice. Coincidently with the development of the psychic 

 secretion there is a dilatation of the gastric blood-vessels and an increase in 

 the supply of blood to the gastric glands. Whether this is due to the action 

 of vaso-dilatator fibers or to an inhibition of the action of vaso-constrictor 

 fibers is uncertain. 



Though the secretion of the gastric juice can be initiated by these means, 

 the amount secreted is but small compared with the quantity secreted after 

 digestion has begun. Then it is that the blood-vessels dilate to their full 

 capacity and furnish for several hours the requisite materials for the pro- 

 duction of the juice on a relatively large scale. That some factor is active 

 in keeping up the secretion in the stomach, is apparent from the in- 

 crease in the quantity and the change in the quality of the juice secreted by 

 the miniature' stomach. 



The secondary stimulus to the gastric secretion is in all probability 

 chemic in character and developed in the stomach or in its walls during 

 digestive activity, inasmuch as the secretion takes place independent of 

 nerve influences and after division of all afferent and efferent nerves that 

 pass from and to the stomach. On the assumption that this factor might 

 be developed in the walls of the stomach itself, Edkins conducted a series of 

 experiments, the results of which lead to the inference that there is developed 

 in the pyloric mucous membrane, by the action of certain articles of food, 

 e.g., dextrin, meat broths, soups, etc., or by the first products of digestive 

 activity, a chemic agent, which is absorbed by the blood, is carried to the glands 

 throughout the stomach and which, on reaching the glands, stimulates their 

 cells in a specific manner. For this reason it has been called the gastric 

 hormone or the gastric secretin. Whatever the agent or the mechanism may 

 be, there is not only an increase in the quantity but a change in the quality 

 of the juice in accordance with the character of the food; in other words, 

 there is an adaptation of the juice to the kind of food to be digested. Thus 

 the protein of bread causes a secretion of five times more pepsin than the 

 same amount of the protein of milk, while the protein of meat causes a 

 secretion of 25 per cent, more pepsin than milk. Meat extract and bouillon 

 have a very stimulating effect on the quantity of juice produced, while alkalies 

 have an inhibitor effect 



Histologic Changes in the Gastric Cells during Secretion. During 

 the periods of rest and secretor activity the cells of the gastric glands undergo 

 changes in histologic structure which are believed to be connected with the 

 production of the enzymes, pepsin and rennin, and the acid. In the resting 

 period the protoplasm of the chief or central cells of the preantral or cardiac 

 glands becomes crow r ded with large and well-defined granules, which during 

 the period of secretory activity largely disappear, so much so that only the 

 luminal border of the cell is occupied by them, the outer border being clear 

 and hyaline in appearance. The parietal cells during rest are large and 

 finely granular, but after secretion they are smaller in size though still granu- 

 lar. (See Fig. 76, A and B.) 



The cells of the pyloric glands, though containing granules, do not show 



