ON SECRETION. 95 



tympani, and to the parotid by a nerve which springs 

 directly from the auriculo-temporal, ultimately, like the 

 chorda, from the facial. The submaxillary may be excited 

 to normal action by direct faradization of the chorda, in 

 which case it pours out its secretion in abundance, and 

 with such force, that if its duct is occluded, its internal 

 surface is exposed to a pressure which may exceed the 

 arterial. In addition to this, excitation of the chorda 

 produces dilatation of the arteries of the gland, in conse- 

 quence of which its supply of blood is largely increased. 

 It can, however, be shown that each of these two effects is 

 independent of the other. During excitation, the tem- 

 perature of the gland rises and the secreting cells undergo 

 important changes (in the dog, disappearance of the 

 " mucous cells " or discharge of their contents, multi- 

 plication or regeneration of the " protoplasm-cells "). 

 The submaxillary gland can also be made to secrete by 

 excitation of the vaso-constrictor nerves which accompany 

 its arteries ; the product so obtained is of high specific 

 gravity and contains much mucus. Severance of all the 

 nerves of the gland produces a continuous discharge of 

 watery liquid which continues for some time. 



The pancreas. During the intervals of digestion the 

 pancreas is inactive. It begins to secrete immediately 

 after food is taken and attains its greatest activity towards 

 the end of gastric digestion. At this time it is red and 

 turgid, and is richest in the material to which its secretion 

 owes its digestive activity ; its cells are larger than before 

 and contain a granular material, which as secretion goes 

 on disappears, but is subsequently regenerated. Nothing 

 is known as to the channels by which the nervous system 

 influences the process. The gastric glands are normally 

 brought into activity by the presence of food or of saliva 

 in the stomach. Their secretion ceases when the stomach 

 is empty, but can be readily excited by mechanical and 

 chemical stimuli, particularly by alkaline liquids. It is 



