5 1 8 THE SALIVAR ) ' 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 How of the saliva 
secreted. 
The current of rest may he either outgoing or ingoing. It is 
usually outgoing in the submaxillary gland of the clog, 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 flow of saliva will 
cause a strong outgoing current. When 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 - 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- 
