288 ACTION OF NERVES ON THE SECRETION OF SALIVA, 



(3.) The pressure in the excretory duct of the salivary gland measured by 

 means of a manometer tied into it may be nearly twice as great as the pressure 

 within the arteries of the glands (Ludwig), or even in the carotid itself. The 

 pressure in Whar ton's duct may reach 200 mm. Hg. 



(4.) Just as in the case of muscles and nerves, the salivary glands become fatigu ad 

 or exhausted after prolonged action. This result may also be brought about by in- 

 jecting acids or alkalies into the duct, which shows that the secretory activity of the 

 gland is independent of the circulation (Gianuzzi). 



[The vascular dilatation and the increased flow of saliva due to the 

 activity of the secretory cells, produced by stimulation of the chorda 

 tympani, although they occur simultaneously, do not stand in the rela- 

 tion of cause and effect. We may cause vascular dilatation without an 

 increased flow of saliva, as already stated (2). If atropin be given to 

 an animal, stimulation of the chorda produces dilatation of the blood- 

 vessels, but no secretion of saliva. Atropin paralyses the secretory 

 fibres, but not the vaso-dilator fibres (Fig. 120). The increased supply 

 of blood, while not causing, yet favours the act of secretion, by placing 

 a larger amount of pabulum at the disposal of the secretory elements, 

 the cells.] 



[The experiment described under (3.) proves, in a definite manner, 

 that the passage of the water from the blood-vessels, or at least from 

 the lymph into the acini of the gland, cannot be due to the blood- 

 pressure; that, in fact, it is not a mere process of filtration, such as 

 occurs in the glomeruli of the kidney. In the case of the salivary gland, 

 where the pressure within the gland may be double that of the arterial 

 pressure, the water actually moves from the lymph against very great 

 resistance. We can only account for this result by ascribing it to the 

 secretory activity of the gland-cells themselves. Whether the activities 

 of the gland-cells, as suggested by Heidenhain, are governed directly 

 by two distinct kinds of nerve-fibres, a set of solid-secreting fibres, and 

 a set of water-secreting fibres, remains to be proved.] 



All these facts lead us to conclude that the nerves exercise a direct effect upon 

 the secretory cells, apart from their action on the blood-vessels. This physiological 

 consideration goes hand in hand with the anatomical fact of the direct continuation 

 of nerve-fibres with the secretory cells. When the chorda tympani is extirpated 

 on one side in young dogs, the sub-maxillary gland on that side does not develop 

 so much its weight is 50 per cent, less while the mucous cells and the "crescents" 

 are smaller than on the sound side (Bufalini). 



During secretion, the temperature of the gland rises 1'5C (Ludwig), 

 and the blood flowing from the veins is often warmer than the arterial 

 blood. 



"Paralytic Secretion" of Saliva. By this term is meant the continued 

 secretion of a thin watery saliva from the sub-maxillary gland, which 

 occurs 24 hours after the secretion of the cerebral nerves (chorda of the 

 seventh), i.e., those branches of them that go to this gland, whether the 



