390 DIGESTION 



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 much 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 cat's cervical sympathetic contains so many vaso-dilator 

 fibres for the submaxillary gland that the usual effect of its stimu- 

 lation with a weak interrupted current is a marked augmentation 

 in the blood-flow affords an explanation. In accordance with this 

 functional similarity, there is a much smaller difference in the action 

 of atr opine on the two sects 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 points 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 

 chorda tympani is stimulated with currents of varying strength, 

 the quantity of organic substances in small samples of saliva 

 collected from a fresh gland is more nearly proportional to the rate 

 of secretion than is the quantity of water and salts, which varies 

 also with the blood-supply. 



Lest the apparently insignificant result of artificial stimulation 

 of the sympathetic in such animals as the dog should cause its 



