262 SECRETION OF GASTRIC JUICE. [BOOK 11. 



animals a similar contrast prevails, though with minor differences. 

 Thus in the rabbit both chorda saliva and sympathetic saliva are 

 limpid and free from mucus, and in the cat, chorda saliva is more 

 viscid than sympathetic saliva; but in both these cases, as in the 

 dog, stimulation of the chorda causes a copious flow with dilated 

 blood-vessels, and stimulation of the sympathetic, a scanty flow 

 with vascular constriction. We shall return again presently to 

 these different actions of the two nerves ; meanwhile we have seen 

 enough of the history of the submaxillary gland to learn that 

 secretion in this instance is a reflex action, the efferent impulses of 

 which directly affect the secreting cells, and that the vascular phe- 

 nomena may assist, but are not the direct cause of, the flow. We 

 have dwelt long on this gland because it has been more fruitfully 

 studied than any other. But the nervous mechanisms of the other 

 secretions are in the main features similar. 



Thus the secretion of the parotid gland, like that of the sub- 

 maxillary, is governed by two sets of fibres: one of cerebro-spinal 

 origin, running along the auriculo-temporal branch of the fifth 

 nerve but originating either in the glosso-pharyngeal or the facial, 

 and the other of sympathetic origin coming from the cervical 

 sympathetic. Stimulation of the cerebro-spinal fibres produces a 

 copious flow of limpid saliva, free from mucus, the secretion 

 reaching in the dog a pressure of 118 mm. mercury ; stimulation of 

 the cervical sympathetic gives rise in the rabbi t to a secretion free 

 from mucus but rich in organic matter and of greater amylolytic 

 power than the cerebro-spinal secretion, but 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 glosso-pharyngeal produces by reflex action a secretion of the 

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



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 stimu- 

 lated. 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 



