1908. | Innervation in Vaso-motor Reflexes, ete. 363 
With respect to the effect of the drug on the excitation phase of the two 
kinds of vascular refiex there is little to be said. I have been unable to 
detect any indication of change of sign before disappearance ; which 
abolition takes place with a less dose of the drug in the case of the constrictor 
centres than of the dilator centres. It seems also that both the above are 
paralysed in respect of response to the normal excitation by a less dose than 
an respect of response to the reversed inhibition, now acting as excitation. 
It remains to refer briefly to the action of strychnine on the Lovén 
reflexes. In the experiment of fig. 8 it was found, after section of all dorsal 
roots supplying dilators to one limb, that a dilator reflex could still be 
obtained by exciting the central end of one of these roots. This proves that 
inhibition of constrictor tone is a factor in these reflexes. In this same 
experiment, later on, a small dose of strychnine was injected into a vein. 
‘On exciting again the same root which had given, previously, dilatation of 
the leg, a constriction was observed. Accordingly, reversal is produced here 
as in the general vascular reflexes. The only point to be noted is that the 
dose of the drug was not sufficient to completely abolish the pressor reflex 
from the median nerve; it is to be remembered, however, that the dog is 
‘very sensitive to strychnine. 
Evidence has already been adduced to show that the rise of arterial pressure 
on excitation of the depressor after strychnine, although caused by excitation 
of the vaso-constrictor centre, is of a somewhat different nature from that due 
to excitation of a pressor nerve under normal conditions. In order to 
obtain more decisive evidence on this point, which seemed of some 
importance, the following experiment was performed. In a cat the spinal 
cord was transected at the second lumbar segment, to cut off the hind limbs, 
one of which was in a plethysmograph, from the dilator centre. Excitation 
of the median nerve produced the usual result of rise of blood-pressure and 
constriction of the leg. Five milligrammes of strychnine were now given 
intravenously. On repeating the excitation of the median nerve no effect 
whatever was produced on the arterial pressure, although the nerve was 
dissected out further and the electrodes placed on a fresh spot. If this 
absence of effect were due to simultaneous excitation of dilators, rather than 
to paralysis of the pressor synapse with the constrictor centre, the con- 
striction should have shown itself in the limb, where there were no dilators 
to mask it. Nothing of the kind was seen, however; the limb remained 
stationary. The conclusion seems justified that the paralysis is a genuine 
one, although I admit that the result, being of a negative character, is not 
absolutely cogent. At this stage of strychnine action, it was found that the 
central end of the vagus still produced fall of pressure, although less than 
