1908. | Innervation in Vaso-motor Reflexes, ete. 361 
Having adopted as a working hypothesis that of Sherrington, I was some- 
what surprised, not to say disconcerted, to find that in the “ dilator” animal 
there is, at a particular stage in the action of the drug, a fall of blood- 
pressure on exciting the central end of the median nerve. It is difficult to 
specify the exact stage, except that a large dose does not seem necessary. Of 
course, in these experiments care was taken to compare the action of stimuli 
of the same strength, since it sometimes happens that weak stimuli may 
cause fall of arterial pressure in the normal animal. This fact is, as yet, 
unexplained ; perhaps it may depend on the presence of depressor fibres 
which are more excitable. In my experiments this effect was not often met 
with, perhaps because curare was used. It seems to have some relation to the 
reflex contractions of voluntary muscle. 
Fall of arterial pressure from excitation of a pressor nerve is a 
characteristic of an advanced stage of the action of chloroform, and is due, 
in this case, to conversion of excitation of constrictors to inhibition of their 
centre. Since the general action of strychnine is antagonistic to that of 
chloroform, it is puzzling to find the same effect produced. 
_ The clue is given by the plethysmograph. Fig. 19 shows that dilatation of 
the kidney is produced after strychnine under conditions which ordinarily 
cause constriction and fig. 20 that, under the same conditions, excitation of 
hy Ny 
: \M Ch | 
Fie. 19.—Vaso-dilatation in kidney from Fie. 20.—Excitation of dilators to ear 
excitation of the median nerve after by “pressor” reflex after strychnine, 
strychnine. Upper curve, volume of which has converted the reflex into a 
the organ. Lower curve, arterial pres- depressor one. Upper curve, volume 
sure. of ear. Lower curve, arterial pressure. 
dilators results. In this experiment, the cervical sympathetic having been 
cut, the large expansion observed on excitation of the median must be due to 
