INFLUENCE OF NERVOUS SYSTEM ON DIGESTIVE GLANDS 395 



the sympathetic strongly, excited, the scanty secretion (if there is 

 any) is of sympathetic type, thick and rich in organic matter. With 

 strong stimulation of both nerves, the secretion, at first plentiful 

 and watery, soon diminishes, even below the amount obtained by 

 stimulation of the chorda alone, because of the diminution in the 

 blood-flow, and therefore in the oxygen-supply, produced by the 

 vaso -constrictors of the sympathetic (Heidenhain). With stimula- 

 tion just strong enough to cause secretion when applied separately 

 to either nerve, there is no secretion when it is applied simul- 

 taneously to both. 



All this refers to the dog. In this animal, then, there seems to be 

 a certain amount of physiological antagonism between the secretory 

 action of the two nerves. But it differs in one respect from the 

 antagonism between their vaso-motor fibres; for with strong stimu- 

 lation the constrictors of the sympathetic always swamp the dilators 

 of the chorda, while the secretory fibres of the chorda appear upon 

 the whole to prevail over those of the sympathetic. And in all 

 probability this apparent secretory antagonism is very superficial, 

 and is due largely to the difference in the vaso-motor effects of the 

 two nerves. For it has been shown that, when the blood- flow 

 through the submaxillary gland is artificially diminished by gradu- 

 ated compression of its artery, stimulation of the chorda gives rise 

 to a thick, viscid and scanty saliva, relatively rich in organic solids 

 (Heidenhain). When the amount of blood passing through the 

 gland is made approximately the same as during stimulation of the 

 sympathetic, the chorda saliva becomes practically identical in 

 composition with the sympathetic saliva. This is one reason, 

 perhaps the chief one, why the sympathetic, when both nerves are 

 stimulated together, without artificial interference with the blood- 

 supply, always appears to add something to the common secretion 

 when there is a secretion at all, this something being represented 

 by an increase in the percentage of organic matter. The observation 

 that the sympathetic effect persists after stimulation has been 

 stopped, and that excitation of the chorda after previous stimula- 

 tion of the sympathetic causes a flow of saliva richer in organic 

 matter than would have been the case if the sympathetic had not 

 been stimulated, has long been considered a proof that the secretory 

 fibres of the two nerves are widely different in function. To explain 

 this result, Heidenhain assumed the existence in the sympathetic 

 of a preponderance of fibres concerned in the building up in the 

 cells of the organic constituents of the saliva (so-called ' trophic/ 

 or, better, since the word ' trophic ' is usually associated with the 

 building up of the bioplasm itself, ' trophic-secretory ' fibres). It 

 would seem, however, that the increase in organic constituents is 

 only realized when a sufficient time has not been allowed, after 

 stimulation of the sympathetic, for the normal circulation to become 

 re-established in the gland. The saliva obtained by stimulation of 



