916 THE EXTERNAL SECRETIONS 



the other hand, requires 0.86 c.c. of oxygen per minute and yields 

 6.39 c.c. of carbon dioxid. 



It has also been noted that the activity of the salivary glands is ac- 

 companied by changes in their electrical potential which originate in the 

 formation of electrolytes and their movements through animal mem- 

 branes. These differences are similar to those observed in active 

 muscle and nerve, and may be detected by applying the poles of a gal- 

 vanometer to the surface and the hilum of the gland. The surface is 

 then galvanometrically positive. In the case of the submaxillary 

 gland, the stimulation of the chorda tympani first increases and then 

 decreases this positivity, which fact signifies that this current pos- 

 sesses a diphasic character. The one evoked by the stimulation of the 

 sympathetic nerve, on the other hand, presents itself merely as a 

 negative variation of the current of rest. 



The Action of Drugs upon the Secretion of Saliva. — If atropin is 

 administered intravenously or is injected into the duct of the sub- 

 maxillary gland, the stimulation of the chorda tympani soon ceases to 

 produce its characteristic secretory effect. Meanwhile, however, the 

 excitation of the sympathetic nerve remains effective and much larger 

 doses of this alkaloid are required to abolish the flow of this type of 

 saliva. The vaso-dilator action of the chorda also persists until 

 additional doses have been administered. This peculiar result sug- 

 gests that atropin paralyzes the endings of the cerebral autonomic 

 fibers, but does not affect the secreting cells themselves. Secondly, 

 it points toward a definite chemical difference between the nervous 

 elements constituting the cerebral or parasympathetic system and 

 those forming the sympathetic system proper. Pilocarpin evokes 

 a copious flow of saliva which is accompanied by vaso-dilatation. 

 This agent, therefore, possesses an antagonistic action to the preceding 

 one and stimulates the endings of the cerebral nerve. Ergotoxin para- 

 lyzes the synnpathetic mechanism, but does not affect the one 

 controlled by the chorda tympani. This fact, again, speaks for the 

 previous contention that the cerebral and sympathetic autonomic fibers 

 differ from one another in their chemical constitution. Adrenalin 

 evokes a constriction of the blood-vessels which, in some animals, is 

 soon followed by a vaso-dilatation and a considerable flow of saliva. 



Nicotin may be used to abolish the action of the secretory nerves, 

 but since it does not affect the secreting cells nor the nerve terminals, 

 it must produce this effect in an indirect way. It is a well-known 

 fact that it destroys the synapses and hence, may be employed to cause 

 a functional discontinuity between the preganglionic and postgan- 

 glionic paths. Thus, if the submaxillary (sublingual) ganglion is 

 moistened with a solution of this alkaloid, the stimulation of the chorda 

 tympani centrally to this ganglion ceases to evoke a secretion from the 

 sublingual gland, because the fibers destined for this organ are relayed 

 at this point. ^ Moreover, inasmuch as this procedure does not block 

 ^Langley, Proc. R. Soc, London, 1889. 



