304 MATHEWS. 



eral stimulations follow closely, one upon the other, the amount 

 of saliva secreted at each stimulation rapidly diminishes and 

 often becomes nothing. Stimulation becomes then again effec- 

 tive if the gland be allowed to rest, if the chorda be irritated, or 

 if liquid be injected into the gland duct. Finally, sympathetic 

 secretion is invariably accompanied by vascular constriction, and 

 the saliva, with the doubtful exception of that of the cat,'^' con- 

 tains more organic matter than that secreted from the same 

 gland under the influence of the dilator nerve. 



That there are deviations from the typical course of a sympathetic secretion just 

 sketched need hardly be said. .Such deviations are probably due (seep. 309) to 

 the changing fluidity of the saliva. When the saliva is thin, as in the horse, rabbit, cat 

 or sheep, the secretion follows a very typical course ; if the saliva be viscous, as in 

 the resting salivary glands of the dog, the latent period is longer, and the secretion 

 persists longer. These variations shed a not unimportant light on the mechanism 

 of secretion. 



To explain these typical phenomena, assuming the secretory 

 activity of the gland cell, Heidenhain supposed that the sympa- 

 thetic nerve carried three kinds of fibres : trophic, secretory and 

 vaso-constrictor. The trophic fibres converted large quantities 

 of mucinogen (submaxillary) into soluble mucin, making the 

 juice rich in organic bodies ; the secretory fibres caused secretion ; 

 the constrictor neutralized the secretory action and stopped 

 secretion. The quick failure of the nerve on successive stimu- 

 lations was referred to the exhaustion of nerve, nerve end, or 

 gland cell. 



The general features of syinpatJietic secretion seem to nu\ hoiv- 

 ever^ plainly to suggest that the secretion lias been driven from the 

 gland by a compression of the ducts and alveoli by some contractile 

 tissue.. I wish to consider these features separately, from this 

 point of view, together with experiments bearing on their proper 

 interpretation. 



a. The Rate of Sympathetic Secretion. 



Experiments I. and II. 



Cat and dog. Submaxillary. Animals under ether. Canula 

 in Wharton's duct, connected with a narrow tube graduated in 

 millimeters, 250 mm. = 0.82 cc. Reading's every ten seconds 



