5 1 2 THE SALIVAR Y GLAXDS. 
It may, however, lie doubted whether there is such a difference in the 
maximum pressure. In the observations I have made on the point, 
stimulating alternately the chorda tympani and the sympathetic, the 
sympathetic has given a perceptible though slight and brief rise of 
pressure at approximately the maximum pressure obtainable from the 
chorda tympani. 
Reflex Inhibition of the Salivary Secretion. 
During the progress of secretion, a certain decrease in the rate of 
flow, or even a cessation, may be caused by stimulation of afferent 
nerves. Such an effect might be due — to select the most probable 
causes — either to an inhibition of the central secretory centre, or to a 
constriction of the blood vessels of the gland. The experiments have 
not, however, been directed to an accurate determination of the method 
of production of reflex inhibition. 
Pawlow 1 states that the slow secretion induced by partial dyspnoea, 
or by curari, is decreased or temporarily stopped by stimulation of the 
sciatic for one or two minutes with a particular strength of current, or 
by exposure of the abdominal viscera. The experiments given can 
hardly be considered to be conclusive, and Buff 2 finds that, quite apart 
from stimulation, the secretion occurring in the conditions of Pawlow's 
experiments is not itself constant in rate. 
Action of Alkaloids upon the SalivaPvY Glands. 
There are obviously a number of ways in which a substance intro- 
duced into the blood might cause a secretion of saliva. It might 
stimulate the peripheral endings of sensory nerves and produce a reflex 
secretion : it might stimulate some part of the central nervous system, 
the connections of the visceral nerve-fibres with the local nerve-cells, 
the neiwe-cells directly, the nerve-endings in the gland, or finally the 
gland-cells directly. Of several of these modes of action we have no 
certain example. "We shall confine our attention to those alkaloids, 
the effects of which have most served as a basis of physiological 
deduction. 3 
Atropine.— Atropine arrests the normal secretion from the glands 
of the mouth, nose, and pharnyx, so that the whole mucous membrane 
becomes dry. The arrest is due to a paralysis of the cranial secretory 
nerves, the strongest stimulation of them no longer causing a secretion.* 
In the dog, 10 to 15 mgrms. of atropine, when injected into a vein, pro- 
duce the paralysis; in the cat, 3 to 5 mgrms. are sufficient. Considerably 
smaller doses than these reduce to very small limits the secretory power 
of the nerves; hence, in determining the minimal amount of atropine 
required to produce paralysis, it is advisable to stimulate the nerve for 
a minute or more, and to repeat this after a few minutes' interval. 
The sympathetic nerve is either not paralysed at all, or only by a 
1 Arch./, d. gcs. Physiol., Bonn, 1S7S, Bd. xvi. S. 272 (experiments made on the sub- 
maxillary gland of the dog). 
2 £e>rr'.z. Anat. u. Physiol. {Eel-hard), Giessen, 1S88, Bd. xii. S. 3. 
3 A few only of the original papers dealing with this subject can be given here ; fuller 
references will be found in treatises on pharmacology. 
4 Keuchel, "Das Atropin und die Hennnungsnerven,'* Dorpat, 1868; Heidenhain, 
Arch.f. d. ges. Physiol., Bonn, 1872, Bd. v. S. 309. 
