332 MATHEWS. 



the observations of Ranvier,*^^ Joseph"'' and others certain secre- 

 tions of sweat are probably due to the compression of the gland 

 by this muscle. Probably the post-mortem sweat secretions, 

 secretion after closing the artery, or the injection of strychnia 

 are due to this cause. (There is, however, a second sweat 

 mechanism associated with vaso-dilation.) 



Many more examples of the muscular mechanism of secretion 

 might be given, but these suffice to indicate the very wide dis- 

 tribution of such a mechanism. Muscular mechanisms are, pos- 

 sibly, more common among the inv^ertebrates, but they play, 

 also, a not inconsiderable part in vertebrate secretions. The 

 vertebrate, however, with its delicately coordinated, closed vas- 

 cular system, develops a second mechanism, that of osmosis, 

 which we will now consider. 



IV. SALIVARY SECRETION ENSUING UPON STIM- 

 ULATION OF THE VASO-DILATOR NERVE. 



That the general features of chorda secretion coincide with 

 the phenomena of osmosis, regulated by the nerve's dilator action, 

 is pointed out briefly on p. 356. I wish here to consider more 

 particularly those facts which have hitherto been irreconcilable 

 with such a theory, and have been generally considered evidence 

 of a special action of the nerve on the gland cell. These facts 

 are the most important evidences of a secretory nerves and so 

 warrant a cai'eful consideration. They are : {ci) the increase in 

 the percentage of organic solids of a secretion coincident with an 

 increased rate of secretion ; (p) the action of atropine ; (r) the 

 chorda-secretion after clamping the artery*; (^) the action of 

 nicotine. 



a. The Increase in the Percentage of Organic Constitu- 

 ents COINCIDENT WITH AN INCREASED RaTE OF SeCRETION. 



Heidenhain * observ^ed that on passing from a weak to a strong 

 stimulation of the dilator nerve in the fresh submaxillary and 



* Heidenhain. Hermann's Handbuch der Physiologie V. p. 50. Studien aus 

 Breslan IV, 1868, p. 32. 



