1908. | Innervation in Vaso-motor Reflexes, ete. 347 
antidromic in nature, I did not think it worth while to devote much time to 
the detailed investigation of the case. 
An indirect piece of evidence, tending to confirm the thesis of this section, 
is derived from consideration of the vascular reflexes in the “eviscerated ” 
animal. In an animal from which all the 
abdominal viscera have been removed or 
tied off from the circulation, and in which, 
also, the abdominal and cervical sympathetics 
have been cut and the median nerve of one 
fore-limb prepared for excitation, it 1s sur- 
prising to find that the changes of blood- 
pressure in vascular reflexes are, in many 
cases, as large as in the normal animal. 
When we remember that the only organs re- 
taining their constrictor supply are one fore- 
limb and part of the other, together with the 
walls and skin of the chest and upper part 
of the abdomen, it is difficult to conceive 
Fie. 3.—Excitation of dilators to 
ear in depressor reflex. Upper 
that this small fraction of the total vascular curve, arterial pressure. Middle 
area remaining can be responsible for as Curve, volume of ear. Time in 
‘ ; : 10 sec. intervals. 
large an effect as is obtained in the complete 
animal; of course, the capacity of the vascular system is very greatly 
diminished, but the proportion of the part supplied with constrictors to the 
whole is far less than in the normal animal. On the other hand, the dilator 
supply of the organs remaining, so far as they possess such, is not interfered 
with. Itis, I think, difficult to avoid the conclusion that the dilators take 
part in the reflexes in such cases. Since I shall have frequently to refer to 
the state of affairs in animals in this condition, I shall, for the sake of brevity, 
speak of these as “dilator” animals. It should be mentioned that no change 
in the heart-beat could be detected in the reflexes referred to above. To put 
it shortly, the “dilator ” animal possesses the following parts supplied with 
dilators and devoid of constrictors: head and neck (perhaps excluding 
brain), hind-limbs, and trunk from middle of abdomen; while the re- 
maining parts have both dilators and constrictors, no part having constrictors 
only. 
(11) Inhibition of Constrictors—As already stated, the general opinion is 
that depressor effects are brought about by inhibition of constrictor tone. 
But, so far as I am aware, the proof has not been yet given that vaso- 
dilatation is possible in the complete absence of dilators. Fig. 4 will serve as 
such a proof. This tracing was obtained from a dog in which, for other 
