260 INFLUENCE OF NERVES ON THE SECRETION OF SALIVA. 



THE INFLUENCE OF THE NERVOUS SYSTEM ON THE 

 SECRETION OF SALIVA. 



The Submaxillary Gland. Stimulation of the facial nerve at its 

 root causes profuse secretion of limpid saliva deficient in the specific 

 constituents. At the same time the blood-vessels of the gland undergo 

 , dilatation. The capillaries, in the presence of increased blood-pressure 

 in them, undergo such a degree of dilatation that the pulsating move- 

 ment of the arteries is transmitted into the veins. More than four 

 times as much blood flows back from the vein, which, besides, appears 

 almost bright red in color and contains more than one-third as much 

 oxygen as the venous blood of the unstimulated gland. In spite of the 

 relatively large amount of oxygen in venous blood, the secreting gland 

 consumes absolutely more oxygen than the inactive gland. 



The facial nerve contains two sets of functionally different fibers: 

 (i) true secretory nerves and (2) vasodilatator nerves. It is not per- 

 missible to regard the phenomenon of secretion as a simple result of 

 increased circulatory activity. 



Stimulation of the sympathetic nerve causes the scanty secretion of 

 a viscid, gelatinous, ropy saliva, containing the specific constituents, 

 particularly mucus and the salivary corpuscles, in abundance, and having 

 a specific gravity of from 1007 to 1010. At the same time, with de- 

 crease in the blood-pressure, the blood-vessels of the gland undergo 

 contraction, so that the small amount of blood escapes from the veins 

 with a dark-blue color. 



The sympathetic nerve likewise contains two sets of functionally different 

 nerve-fibers, (i) true secretory fibers and (2) vasoconstrictor nerves. Continued 

 stimulation of the chorda tympani and the sympathetic nerve alters the secretions, 

 making them more nearly alike, and thus teaches that, essentially, the saliva pro- 

 duced by stimulation of the chorda tympani and that produced by stimulation of 

 the sympathetic nerve differ not specifically, but only in degree. With increasing 

 nerve-stimulation the secretion increases, and with it the amount of contained salts. 

 The organic constituents depend, in addition to the intensity of the stimula- 

 tion, upon the condition of the gland, whether at rest or exhausted. The 

 constitution of the blood and the circulatory conditions in the gland likewise 

 influence the composition of the saliva. 



That the secretion of the glands cannot be considered as a simple filtration 

 as the result of changes in blood-pressure, but that it occurs as an independent 

 function in conjunction with changes in the blood-vessels, will appear from the 

 following considerations : 



1. The secretory activity of the gland, on stimulation of the nerves, continues 

 for some time even after all blood-vessels have been ligated. 



2 . Atropin and daturin destroy the activity of the secreting fibers in the chorda 

 tympani, but not that of the vasodilator fibers. 



3. The pressure in the excretory ducts of the salivary glands, which can be 

 measured by means of a manometer tied in the duct, may be almost twice as 

 great as that in the arteries of the gland, having reached about 290 mm. of mercury 

 in the excretory duct of the submaxillary gland. With increase in the pressure 

 the amount of saliva diminishes, as does likewise the amount of work performed 

 by the gland. 



4. The salivary glands, in the same way as nerves and muscles, also fatigue, 

 especially after injection of acids or alkalies into the excretory duct. This indi- 

 cates that the secretory structure is independent of the circulation and under the 

 influence of the nerves. 



5. That in the secretion of saliva the cellular activity of the glands also is 

 evident is shown by the researches of Zerner, who, after intravenous injection of 

 indigo-carmine, found this substance within the mucous cells and the rod-cells. 



It must, therefore, be inferred that the nerves exert a direct influence on the 



