5 1 8 THE SALIVAR Y GLANDS. 



gland itself from the gland-cells to the surrounding tissue the current 

 is an ingoing current. When the outer surface of the gland is negative 

 to the hilus, so that the direction of the current in the galvanometer 

 circuit is from the hilus to the outer surface, and in the gland itself 

 from the gland-cells towards the duct, the current is outgoing. The 

 outgoing current, then, is one in the direction of the flow of the saliva 

 secreted. 



The current of rest may be either outgoing or ingoing. It is 

 usually outgoing in the submaxillary gland of the dog, and usually ingoing 

 in the submaxillary gland of the cat. The causes of the difference of 

 direction have not been determined. 



Any stimulation of nerves which causes a rapid now of saliva will 

 cause a strong outgoing current. Wheif the flow of saliva is slight, the 

 current, as a rule, is either diphasic, first outgoing and then ingoing, or 

 ingoing only. Thus in the submaxillary or parotid gland of the dog, 

 stimulation of the cranial nerve causes an outgoing current, and stimula- 

 tion of the sympathetic, provided the secretion be slight, causes an 

 ingoing current. The ingoing current begins less quickly and is less 

 strong than the outgoing current. 



In the submaxillary gland of the dog, the current of rest is said to vary 

 from 1-500 to 1-10 of a volt. The outgoing current, caused by stimulating the 

 chorda tympani, begins about 0*37 seconds after the beginning of the stimu- 

 lation, and before saliva appears in the duct ; it reaches its maximum before 

 the maximum rate of secretion is attained. It may undergo temporary 

 diminution or reversal, indicating the development of an ingoing current. 

 The ingoing current, caused by stimulating the sympathetic, begins two to 

 three seconds after the beginning of the stimulation, and only slowly attains 

 its maximum. 



In the submaxillary gland of the cat, stimulation, either of the chorda or 

 of the sympathetic, causes, in most cases, first an outgoing and then an ingoing 

 current. 



Atropine annuls the effect of nerve stimulation, except perhaps in 

 the case of the sympathetic of the dog ; here the ingoing current pro- 

 duced by stimulation is much reduced, but it is not clear that it is com- 

 pletely abolished even by 100 mgrms. of atropine. Atropine annuls the 

 outgoing current of stimulation before the ingoing. The amount of 

 atropine required to abolish the outgoing current of stimulation is approxi- 

 mately that required to render the flow of saliva very slight. The 

 amount of atropine required to abolish the ingoing current of stimulation 

 is approximately that required to paralyse completely the secretory 

 activity of the nerve stimulated (cf. p. 512). 



Bradford attributes the ingoing current to "changes in the gland 

 cells, leading to the elaboration of the organic constituents of the saliva," 

 these being caused by the action of Heidenhain's trophic fibres, and 

 thinks that the outgoing current is probably due " either to the passage 

 of the fluid part of the secretion through the walls of the alveoli, or to 

 the changes in the gland structures, that follow the excitation of a 

 secretory nerve and precede the gland flow." 



Most of the facts could be accounted for by supposing that the outgoing 

 current is due to physical causes, namely, due to the passage of fluid through the 

 gland-cells ; and that the ingoing current is due to chemical causes, namely, the 

 metabolic changes in the gland-cells, but the questions involved are too com- 



