396 DIGESTION 



the chorda immediately after a period of artificially diminished 

 blood-flow, without any previous excitation of the sympathetic, 

 also contains a surplus of organic matter (Carlson). 



Indeed, the distinction between chorda and sympathetic saliva, 

 which, by taking account of the parotid as well as the submaxillary 

 and sublingual glands, has been generalized into a distinction 

 between cerebral and sympathetic saliva, and which, when the 

 vaso-motor conditions are left out of account, appears to hold good 

 in the dog and the rabbit, breaks down before a wider induction. 

 For in the cat the sympathetic saliva of the submaxillary gland, 

 although more scanty, is more watery than the chorda saliva 

 (Langley), which, however, is by no means viscid; and the two 

 secretions differ far less than in the dog. The discovery of Carlson 

 that the usual effect of stimulation of the cat's cervical sympathetic 

 with a weak interrupted current is a marked augmentation in the 

 blood-flow* through the submaxillary gland affords an explanation. 

 In accordance with this functional similarity, there is a much 

 smaller difference in the action of atropine on the two sets of fibres 

 in the cat than in the dog, although even in the cat the sympathetic 

 is less readily paralyzed than the chorda. 



In their secretory action there is not even an apparent antagonism 

 in the cat, with minimal stimulation of both nerves, which causes 

 as much secretion as would be produced if both were separately 

 excited. Further, even in the dog, after prolonged stimulation of 

 the sympathetic, the submaxillary saliva is no longer viscid, but 

 watery, the proportion of solids, and especially of organic solids, 

 being much lessened, as it is also in chorda saliva after long excita- 

 tion. When the cerebral nerve of the resting gland is strongly 

 excited, it is found that up to a certain limit the percentage of 

 organic matter in a small sample of saliva subsequently collected 

 during a brief weak excitation increases with the strength of the 

 previous stimulation; this is also true of the inorganic solids. But 

 there is a striking difference when the experiment is made on a gland 

 after a long period of activity; here increase of stimulation causes 

 no increase in the percentage of organic material, while the inorganic 

 solids are still increased. In both cases the absolute quantity of 

 water, and therefore the rate of flow of the secretion, is augmented. 



All this pojnts to the same conclusion as the microscopic appear- 

 ances in the gland-cells, that the cells during rest manufacture the 

 organic constituents of the secretion, or some of them, and store 

 them up, to be discharged during activity. The water and the 

 inorganic salts, on the other hand, seem rather to be secreted on 

 the spur of the moment, so to speak, and not to require such 

 elaborate preparation. And it has been stated that when the 



* The increased blood-flow, which can be even better elicited by injection of 

 adrenalin, immediately succeeds the secretion of saliva, and seems to be due 

 not to the presence of vaso-dilator fibres in the sympathetic, but to metabolic 

 product*. 



