510 ELECTRO-PHYSIOLOGY CHAP. 



They appear to have succeeded in the demonstration attempted 

 by Hermann and Lnchsinger (79), of the secretion currents in 

 these glands. During rest the surface of the exposed submaxillary 

 gland of the dog was, as a rule, negative to the hilus. The 

 E.M.F. of this current of rest, which must be referred, not 

 to the injured region (muscles), but to the gland itself, varies 

 within a wide range in different individuals, as also in the same 

 animal at different times. The altering relations within the 

 gland would seem to be the cause of this as is attested by the 

 fact that permanent changes of the current of rest are induced 

 not merely by temporary excitation of the gland nerves, but 

 also by atropin poisoning. The direction of the rest current 

 varies much more (being indeed frequently reversed) in the sub- 

 maxillary of the cat than in the dog (surface positive to hilus). 

 This is the more striking, in view of the extensive morphological 

 coincidence of this gland in the two animals, since the rest 

 current of the " serous " parotid gland in the dog generally agrees 

 in direction with that of its submaxillary. 



Hence it would appear that functional differences in the 

 glands regulate the observed differences of potential. The 

 behaviour of the " action current " on exciting the secretory 

 nerve also speaks for the same conclusion. After compensating 

 the current of rest, excitation of the chorda tympani in the dog 

 always causes negativity of the external surface of the sub- 

 maxillary gland. The period of this variation is often interrupted 

 by a second antagonistic phase, which sometimes expresses itself 

 only in a retardation or temporary stand-still of the deflection, 

 while it is frequently masked altogether by the first and more 

 pronounced principal phase. The deflection begins after a short 

 latent period, before any secretion has appeared in the canal, and 

 where the excitation is weak it forms the only manifestation. 



Excitation of the cervical sympathetic also invariably pro- 

 duces electromotive action in the submaxillary glands of the 

 dog, distinguished, however, from the above by smaller effect, 

 longer latent period, and monophasic variation (surface positive 

 to hilus), i.e. the reverse of the principal phase in chorda 

 excitation. 



In the same gland of the cat, on the contrary, the second 

 phase (surface positive to hilum) is the more pronounced with 

 excitation from the chorda. Bayliss and Bradford find unmis- 



