362 Dr. W. M. Bayliss. On Recuprocal [Jan. 20, 
the dilator nerves. Fig. 21 is, perhaps, important, since it shows a similar 
phenomenon in the hind-limb, atter section of both abdominal sympathetics, 
so that there is no possibility of constrictors playing any part. 
These results at once suggest the meaning of the conversion of the 
“pressor” rise into a fall and of its cause, excitation of vaso-dilators. In 
the earlier part of this paper I have shown that in the normal pressor reflex 
there is, along with excitation of constrictors, an inhibition of dilator tone ; 
now, by hypothesis, the action of strychnine is to change in some way a 
process resulting in inhibition into one of excitation ; so that it was really to 
be expected that the drug would effect such a change that dilator excitation 
would result from ordinary sensory nerves. Figs. 22 and 23 show the effect 
Fic. 21.—Excitation of dila- Fie. 22.—Inhibition of dilator Fic. 23.—Excitation of dila- 
tors to hind-leg by reflex tone before strychnine. tors after injection of the 
from median nerve after drug. In both figures the 
strychnine. Upper curve, upper curves are the vol- 
volume of limb. Lower ume of the ear, the lower 
curve, arterial pressure. curves are the arterial 
pressure. 
of excitation of the median nerve, on the rabbit’s ear deprived of con- 
strictors, before and after the injection of strychnine. 
In view of this fact it seems possible that the absence of pressor effects 
from sensory nerves in the “complete” animal after a comparatively small 
dose of the alkaloid may not mean total paralysis of the constrictors but 
a diminution of their excitability only, and that the simultaneous excitation 
of dilators sutfices to antagonise their effect on the general blood-pressure. 
The apparent anomaly of conversion of rise of pressure into fall by the 
action of strychnine turns out to be, in reality, a confirmation of the 
hypothesis adopted. 
