396 THE HUMAN BODY. 



other sets of fibres : one governing the salts and water, and 

 the other the specific elements of the secretion. So far the 

 evidence is, perhaps, not quite conclusive; but experiments 

 upon the parotid gland of the dog put the matter beyond a 

 doubt. 



The submaxillary gland receives fibres from the sympa- 

 thetic system, as well as the chorda tympani from the cerebro- 

 spinal. Excitation of the sympathetic fibres causes the 

 gland to secrete, but the saliva poured out is different from 

 that following chorda stimulation, which is in the dog abun- 

 dant and comparatively poor in organic constituents, and 

 accompanied by vascular dilatation : while the " sympathetic 

 saliva," as it is called, is less abundant, very rich in inucin, 

 and accompanied by constriction of the gland arteries. 

 According to the above view we might suppose that the 

 chorda contains many trausudatory and few trophic fibres, 

 and the sympathetic many trophic and few transudatory. 

 It might, however, well be objected that the greater rich- 

 ness in organic bodies of the sympathetic saliva was really 

 due to the small quantity of blood reaching the gland, when 

 that nerve was stimulated. This might alter the nutritive 

 phenomena of the cells and cause them to form mucin in 

 unusual abundance, in which case the trophic influence of 

 the nerve would be only indirect. Experiments on the 

 parotid preclude this explanation. That gland, like the sub- 

 maxillary, gets nerve-fibres from two sources: a cerebral and 

 a sympathetic. The latter enter the gland along its artery, 

 while the former, originating from the glosso-pharyngeal, 

 run in a roundabout course to the gland. Stimulation of the 

 cerebral fibres causes an abundant secretion, rich in water 

 and salts, but with hardly any organic constituents. At the 

 same time it produces dilatation of the gland arteries. Stim- 

 ulation of the sympathetic causes contraction of the parotid 

 gland arteries and no secretion at all. Nevertheless it causes 

 great changes in the gland-cells. If it be first stimulated 

 for a while and then the cerebral gland-nerve, the resulting 

 secretion may be ten times as rich in organic bodies as that 

 obtained without previous stimulation of the sympathetic; 

 and a similar phenomenon is observed if the two nerves be 

 stimulated simultaneously. So that the sympathetic nerve, 

 though unable of itself to cause a secretion, brings about 

 great chemical changes in the gland-cells. It is a distinct 



