240 AN AMERICAN TEXT- HOOK OF PHYSIOLOGY. 



juice. Finally, these observers were able to show that direct stimulation of 

 the vagi under proper conditions causes, after a long latent period (four and 

 a half to ten minutes), a marked secretion of gastric juice. The long latent 

 period is attributed to the simultaneous stimulation of inhibitory fibres. 



Taking these results together, we must believe that the vagi send secretory 

 fibres to the gastric glands, and that these fibres may be stimulated reflexly 

 through the sensory nerves of the mouth, and probably also by psychical 

 states. 



Normal Mechanism of Secretion of the Gastric Juice. — Our knowl- 

 edge of the means by which the flow of gastric secretion is caused during 

 normal digestion, and of the varying conditions which influence the flow, is 

 as vet quite incomplete. The notable experiments recently made by Pawlow ' 

 and his pupils, together with older experiments by Heidenhain, 2 have, however, 

 thrown some light upon this difficult problem, and have, moreover, opened 

 the way for further experimental study of the matter. Heidenhain cut out 

 a part of the fundus of the stomach, converted it into a blind sac, and brought 

 one end of the sac to the abdominal wall so as to form a fistulous opening to 

 the exterior. The continuity of the stomach was established by suturing the 

 cut cnd>, but the fundic sac was completely separated from the rest of the 

 alimentary canal. This operation has since been modified by Pawlow in such 

 a way that the isolated fundic sac retains its normal nerve supply. Heiden- 

 hain found that under these conditions the ingestion of ordinary food caused 

 a secretion in the isolated and empty fundic sac, the secretion beginning 

 fifteen to thirty minutes after the food was taken, and continuing until the 

 stomach was empty. The ingestion of water caused a temporary secretion in 

 the fundus, while indigestible material such as ligamentum nucha? gave no 

 secretion at all. Heidenhain's interpretation of these experiments as applied 

 to normal secretion was that in ordinary digestion we must distinguish 

 between a primary and a secondary secretion. The primary secretion depends 

 upon the mechanical stimulus of the ingested food, and is confined to the spots 

 directly stimulated ; the secondary secretion begins after absorption from the 

 stomach is in progress, and involves the whole secreting surface. The first 

 part of this theory is in accord with a belief which heretofore has been very 

 generally held by physiologists, namely, that the gastric glands may be made 

 to secrete by direct mechanical excitation. Pawlow has shown, however, by 

 what seem to be most convincing experiments, that this belief is erroneous. 

 Mechanical stimulation, strong or weak, circumscribed or general, seems to be 

 totally without effect in arousing a secretion. Pawlow has been led by his 

 interesting experiments to give a different explanation of the normal mechan- 

 ism of secretion. The first effect of eating is the production of the " psychical 

 secretion," before referred to. This secretion is effected through the action 

 of secretory fibres in the vagus, and possibly also in the sympathetic nerve. It 

 begins usually within five minutes, is, in a general way, proportional in amount 



1 Archives des Sciences biologiques, St. Petersburg, 1895, t. iii. p. 461 ; t. v. p. 425. 

 'Hermann's Handbuch der Physiologie, 1883, Bd. v. S. 114. 



