402 SECRETION OF GASTEIC JUICE. [BOOK n. 



also free from mucus but rich in proteids and of greater amylolytic 

 power than the cerebro-spinal secretion ; in the dog little or no 

 secretion is produced, though, as we shall see later on, certain 

 changes are brought about in the gland itself. In both animals 

 the cerebro-spinal fibres are vaso-dilator, and the sympathetic 

 fibres vaso-constrictor in action. Stimulation of the central end of 

 the glossopharyngeal produces by reflex action a secretion from the 

 parotid gland, but that of the lingual is said to be without 

 effect. 



230. The secretion of gastric juice. Though a certain amount 

 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 the working of a local mechanism ; 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 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 stomach is supplied with nerve-fibres from the two vagi 

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



