314 COMPARATIVE PHYSIOLOGY. 



case of stimulation of the chorda the vessels of the gland are 

 dilated, while in the case of the sympathetic they are con- 

 stricted. 10. If atropin be injected into the blood, it is impos- 

 sible to induce sahvary secretion by any form of stimulation, 

 though excitation of the chorda nerve still causes arterial dila- 

 tation. 



Conclusions. — l. There is a center in the medulla presiding 

 over salivary secretion. 2. The influence of this center is ren- 

 dered efBective through the chorda tympani nerve at all events, 

 if not also by the sympathetic. 3. The chorda tympani nerve 

 contains both secretory and vaso-dilator fibers; the sympathetic 

 secretory and vaso-constrictor fibers. 4. Arterial change is not 

 essential to secretion, though doubtless it usiially accompanies 

 it. Secretion may be induced in the glands of an animal after 

 decapitation by stimulation of its chorda tympani nerve, analo- 

 gous to the secretion of sweat in the foot of a recently dead 

 animal, under stimulation of the sciatic nerve. 5. The char- 

 acter of the saliva secreted varies with the nerve stimulated, so 

 that it seems likely that the nervous centers normally in the 

 intact animal regulate the quality of the saliva through the 

 degree to which one or the other kind of nerves is called into 

 action. 6. Secretion of saliva may be induced reflexly by ex- 

 periment, and such is probably the normal course of events. 

 7. The action of the medullary center may be inhibited by the 

 cerebrum (emotions). 



Some have located a center in the cerebral cortex (taste cen- 

 ter), to which it is assumed impulses first travel from the 

 tongue and which then rouses the proper secreting centers in 

 the medulla into activity. It seems more likely that the corti- 

 cal center, if there be one, completes the physiological processes 

 by which taste sensations are elaborated. 



From the influence of drugs (atropin and its antagonist 

 pilocarpin) it is plain that the gland can be effected through 

 the blood, though whether wholly by direct action on the cen- 

 ter, on any local nervous mechanism or directly, on the cells, is 

 as yet undetermined. It is found that pilocarpin can act long 

 after section of the nerves. This does not, however, prove that 

 in the intact animal such is the usual modus operandi of this 

 or other drugs, any more than the so-called paralytic secretion 

 after the section of nerves proves that the latter are not con- 

 cerned in secretion. 



We look upon paralytic secretion as the work of the cells 



