THE DIGESTIVE SECRETIONS 929 



not inhibito-secretory in its nature, they cannot be considered as 

 forming a part of an inhibitor mechanism which acts antagonistically 

 to the vagi nerves. The latter are secretomotors. It seems, therefore, 

 that the vagi nerves are capable of stimulating as well as of inhibiting 

 the flow of the gastric juice, and hence, they must form the chief 

 efferent secretory path between the central nervous system and the 

 stomach. 



In considering the effects of the intragastric stimuli, we are con- 

 fronted by the statement that the mechanical stimulation of the gastric 

 mucosa produces only a discharge of mucus and not of gastric juice. 

 Even water and meat, when introduced through a fistula, give rise 

 to only a slight flow. The same is true of bread and coagulated white 

 of egg, and especially if these substances are introduced while the 

 animal is sleeping. Of particular interest is the long latent period then 

 intervening between the moment of feeding and the time when the 

 first drop of gastric juice is obtained. Even in the case of raw meat, 

 15 to 45 minutes may elapse before the secretion actually begins, but a 

 somewhat quicker reaction may be evoked by giving these substances 

 in a semi-digested condition, because the purely nervous excitation 

 is then augmented by the liberation of chemical bodies in the form of 

 vitamines and hormones which stimulate the gastric glands either 

 directly or thrgugh the blood. 



A slight secretion of gastric juice is also obtained after the stomach 

 has been isolated from the central nervous system by the division 

 of all of its nerves, namely, the vagi and splanchnic nerves and the com- 

 municating rami of the latter. Consequently, this organ must be in 

 possession of a local reflex mechanism which under ordinary conditions 

 is controlled directly by the central nervous system. In other words, 

 inasmuch as the stomach is a typical autonomic organ, the higher 

 centers merely alter its activity in accordance with the functional 

 requirements of other parts of the body. Impulses are relayed to it 

 which either increase or decrease the flow of gastric juice. 



These data tend to show that the direct stimulation of the gastric 

 receptors is not a very efficient means of evoking a secretion of gastric 

 juice. Much better results may be obtained by influencing the local 

 mechanism through a more general mechanism which is capable of 

 introducing what is termed the psychical element, or appetite. As 

 long ago as 1852, Bidder and Schmidt observed that a copious secre- 

 tion of gastric juice may be evoked in a dog with a gastric fistula by 

 simply allowing him to obtain a visual impression of the food. Some 

 years later Richet obtained the same results in a boy whose esophagus 

 had been completely closed by a cicatrix formed in consequence of 

 an erosion by a strong alkali. Since that time this observation has 

 been repeated a large number of times both upon human beings with 

 gastric fistulas as well as upon different mammals with diverticulated 

 stomachs. Another procedure which has led to valuable results is 



