426 SECRETION OF GASTRIC JUICE. [BOOK n. 



of gastric juice may sometimes be found in the stomachs of fasting 

 animals, it may be stated generally that the stomach, like the 

 salivary glands, remains inactive, yielding no secretion, so long as 

 it is not stimulated by food or otherwise. The advent of food into 

 the stomach however at once causes a copious flow of gastric juice; 

 and the quantity secreted in the twenty-four hours is probably very 

 considerable, but we have no trustworthy data for calculating the 

 exact amount. So also when the gastric mucous membrane is 

 stimulated mechanically, as with a feather, secretion is excited : 

 but to a very small amount even when the whole interior surface 

 of the stomach is thus repeatedly stimulated. The most efficient 

 stimulus is the natural stimulus, viz. food; though dilute alkalis 

 seem to have unusually powerful stimulating effects; thus the 

 swallowing of saliva at once provokes a flow of gastric juice. 

 During fasting the gastric membrane is of a pale grey colour, 

 somewhat dry, covered with a thin layer of mucus, and 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. 



231. 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 a direct local action ; and this view is supported by 

 the fact that when a mechanical stimulus is applied to one spot of 

 the gastric membrane the secretion is limited to the neighbourhood 

 of that spot and is not excited in distant parts. This local action 

 may be nervous in nature or the effect of the stimulus may per- 

 haps 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 suggest the presence 

 of a nervous mechanism. 



The stomach is supplied with nerve-fibres from the two vagi 

 nerves and from the solar plexus of the splanchnic system. The 

 two vagi (see Fig. 70) after forming the oesophageal plexus on the 

 oesophagus are gathered together again as two main trunks which 

 run along the oesophagus, the left in the front, the right at the 

 back, to the stomach. The left, or anterior nerve is distributed to 

 the smaller curvature and the front surface of the stomach, forming 

 a plexus in which nerve-cells are present ; and branches pass on to 

 the liver and probably to the duodenum. The right, or posterior 

 nerve is distributed to the hinder surface of the stomach, but only 

 to the extent of about one-third of its fibres ; about two-thirds of 

 the fibres pass on to the solar plexus. The fibres of the vagus 

 nerves thus distributed to the stomach are for the most part non- 



