1908. | Innervation in Vaso-motor Reflexes, ete. 343 
Chorda tympani. The central end of the vagus, on the opposite side to the 
gland under observation, was arranged for excitation. As a rule, the animal 
was eviscerated, in order to diminish the effects of the mere fall of blood- 
pressure on the rate of flow through the gland. Fig. 1 is a tracing obtained 
in this way. It will be noted that, in spite of evisceration, there is a large 
fall of arterial pressure, which lasts for a long time after the excitation ceases. 
This is usually the case with vaso-motor reflexes in the cat. While the 
blood-pressure is falling, the drops greatly increase in number per unit time, 
but later, the effect of the low blood-pressure shows itself by a slowing of the 
flow. There is, apparently, no lasting vaso-dilatation, as seen in direct 
excitation of the chorda. The reason for this is, probably, that no saliva is 
secreted, so that the action of products of cell-activity on the arterioles is 
Ay f \ 
VAWMMacanseannnh MANY 
RTE TH 
N 
hn, 
iy 
| eer eee ee ee ee 
Fig. 1.—Excitation of chorda dilators in depressor reflex. Upper line, drops of blood 
from gland vein. Middle curve, arterial pressure. Bottom line, time in 
10 sec. Zero of blood-pressure, 58 mm. below time line. 
absent.. In order to save space, the middle part of the tracing has been cut 
out, amounting to three minutes in time. 
A circumstance may be mentioned here that makes the investigation of 
this, as of other vaso-dilator reflexes,a matter of peculiar difficulty: viz., 
they are only to be seen while the animal is in the best condition as regards 
temperature, blood-pressure, etc., z.¢., at the beginning of an experiment. It 
seems improbable that this loss of reflex excitability is due to fatigue, since it 
has no obvious relation to the number of times the reflex has been excited. 
The effect on the submaxillary gland above described is abolished by 
section of the chorda, but considering the circumstance spoken of in the 
previous paragraph, too much importance must not be given to this result. 
