366 A MANUAL OF PHYSIOLOGY. 



of the sympathetic (Heidenhain). With stimulation just strong 

 enough to cause secretion when applied separately to either 

 nerve, there is no secretion when it is applied simultaneously 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 stimulation 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 sympa- 

 thetic. And in all probability this apparent secretory antagonism 

 is very superficial, and is due largely to the difference in the 

 vasomotor effects of the two nerves. For it has been shown 

 that when the blood-flow through the submaxillary gland is 

 artificially diminished by graduated 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, with- 

 out 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 sympa- 

 thetic effect persists after stimulation has been stopped, and 

 that excitation of the chorda after previous stimulation 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 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). 



