CHAP, i.] DIGESTION. 263 



thrown into folds; during digestion it becomes red, flushed, and 

 tumid, the folds disappear, and minute drops of fluid appearing at 

 the mouths of the glands, speedily run together into small streams. 

 When the secretion is very active, the blood flows from the 

 capillaries into the veins in a rapid stream without losing its bright 

 arterial hue. The secretion of gastric juice is in fact accompanied 

 by vascular dilation in the same way as is the secretion of saliva, 

 but the vascular mechanism has not yet been fully worked out, 

 though there is evidence of the vagi nerves being concerned in 

 the matter. 



Seeing that, unlike the case of the salivary secretion, food is 

 brought into the immediate neighbourhood of the secreting cells, it 

 is exceedingly probable that a great deal of the secretion is the 

 result of the working of a local mechanism ; and when a mechanical 

 stimulus is applied to one spot of the gastric membrane the secre- 

 tion is limited to the neighbourhood of that spot and is not excited 

 in distant parts. This local mechanism may be nervous in 

 nature or the effect of the stimulus may perhaps be conveyed 

 directly from cell to cell, from the mouth of the gland to its 

 extreme base without the intervention of any nervous elements ; 

 but the vascular changes at least would seem to imply the presence 

 of a nervous mechanism. 



The importance of this local mechanism and the subordinate 

 value of any connection between the gastric membrane and the 

 central nervous system is further shewn by the fact that a secretion 

 of quite normal gastric juice will go on when both vagi, or when 

 the sympathetic nerves going to the stomach are divided, 

 or indeed when all the nervous connections of the stomach 

 are. severed. And all attempts to provoke or modify gastric 

 secretion by the stimulation of the nerves going to it, have 

 hitherto failed. On the other hand, in cases of gastric fistula, where 

 by complete occlusion of the oesophagus stimulation by the descent 

 of saliva has been avoided, the mere sight or smell of food has 

 been seen to provoke a lively secretion of gastric juice. This 

 must have been due to some nervous action ; and the same may 

 be said of the cases where emotions of grief or anger suddenly 

 arrest the secretion or prevent the secretion which would otherwise 

 have taken place as the result of the presence of food in the 

 stomach. So that much has yet to be learnt in this matter. 



The contrast presented between the scanty secretion resulting 

 from mechanical stimulation and the copious flow which actual 

 food induces is interesting because it seems to shew that the 

 secretory activity of the cells is heightened by the absorption 

 of certain products derived from the portions of food first 

 digested. This is well illustrated by the following experiment of 

 Heidenhain. This observer, adopting the method employed 

 for the intestine (see p. 255), succeeded in isolating a portion 

 of the fundus from the rest of the stomach ; that is to say, he cut 



