76 PHYSIOLOGY CHAP. 



All these phenomena relate to the secretory process in the 

 submaxillary gland of the dog, which has been the subject of 

 innumerable researches. But the same facts (with slight differ- 

 ences) may be observed in other animals also. Thus in the rabbit, 

 the saliva that flows on excitation of the chorda and also that 

 from excitation of the sympathetic are limpid and fluid ; in the 

 cat, the first kind is more viscid than the second. But in both 

 cases excitation of the chorda produces copious secretion and 

 vascular dilatation, excitation of the sympathetic, scanty secretion, 

 and vascular constriction. 



Gerhardt studied the histological changes consequent on 

 section of the secretory nerves on the salivary glands of rabbit, 

 and found substantial differences in the effects of dividing the 

 chorda and the sympathetic. In the former the protoplasm was 

 altered while the nuclei remained intact; in the second, on the 

 contrary, there were marked nuclear alterations with normal 

 protoplasm. The two kinds of histological change were never 

 observed in all the gland cells, but only in foci, without any 

 apparent regularity, partly in big nests, partly isolated. The 

 nuclear alterations from section of the sympathetic were not 

 confined to the side of the section but spread also, although to a 

 minor extent, to the opposite side. 



The nervous mechanism of the other salivary glands is similar 

 in its general features to that of the submaxillary gland, on which 

 we have dwelt at length. Division of Jacobson's nerve or of the 

 small superficial petrosal nerve, or excision of the otic ganglion, 

 arrests the secretion of the parotid gland (Bernard, Schiff, 

 Heidenhain). Excitation of these cranial fibres produces in the 

 parotid the same secretory and vascular effects as that of the 

 chorda tympani in the submaxillary. The pressure measured in 

 Scensen's duct rises during stimulation to 106-118 mm. Hg. 

 The flow of blood from the gland is accelerated and assumes 

 the arterial hue (Heidenhain). The effect of stimulating the 

 sympathetic has, on the contrary, been much disputed. Some 

 deny it, others admit a simple constrictor effect on the parotid 

 vessels, others, lastly, assume a trophic influence upon the gland 

 cells, as distinct from, the secretory influence (Heidenhain). 



The sublingual gland is controlled by the same nerves as those 

 which regulate the secretion of the submaxillary. Stimulation of 

 the chorda tympani excites secretion from the sublingual as well, 

 but requires a stronger stimulus (01. Bernard, Heidenhain). 

 The stimulation of the sympathetic has no perceptible effect. 



III. The most obvious proof that the secretory effect of 

 exciting the nerves is due essentially to their trophic influence 

 upon the metabolism of the secretory gland-cells, is shown under 

 the microscope in the marked changes which these cells undergo 

 during secretory activity. We owe to Heidenhain (1868) this 



