822 ANIMAL’ PHYSIOLOGY. 
nerve. 5. The character 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 experiment, 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 affected 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 
when gone wrong—passed from under the dominion of the 
nerve-centers. Secretion is a part of the natural life-processes 
of gland-cells—we may say a series in the long chain of pro- 
cesses which are indispensable for the health of these cells. 
They must be either secreting cells, or have no place in the nat- 
ural order of things. It is to be especially noted that the secre- 
tion of saliva continues when the pressure in the ducts of the 
gland is greater than that of the blood in its vessels or even 
of the carotid; so that it seems possible that over-importance 
has been attached to blood-pressure in secretory processes 
generally. 
It may, then, be safely assumed that formation of saliva re- 
sults in consequence of the natural activity of certain cells, the 
processes of which are correlated and harmonized by the nerv- 
ous system; their activity being accompanied by an abundant 
supply of blood. The actual outpouring of saliva depends usu- 
ally on the establishment of a nervous reflex arc. The other 
glands have been less carefully studied, but the parotid is 
