PHYSIOLOGICAL ACTION OF VENOM OF BLACK SNAKE, 217 
spleen was obtained, show that both curves decline and rise 
together. The fall in pressure is accompanied by a simultaneous 
and equally abrupt diminution in the volume of the spleen and 
kidney, and in those experiments in which the arterial pressure 
recovered, the volume of these organs increased at the same time, 
and again diminished as the pressure in the arteries finally fell. 
Had vascular dilatation (provided it affected these organs), been 
the explanation of the fall in pressure, the two curves would have 
crossed one another and not run in a parallel direction. 
I think these organs, and especially the spleen, may be taken as 
fair samples of the area in which vascular dilatation due to vaso- 
motor paresis would occur, and this evidence, taken in conjunction 
with the results of the experiments on animals with divided spinal 
cords, justifies the conclusion that the fall in blood pressure is 
cardiac in origin, and that any result of vaso-motor paralysis is 
insignificant in comparison with the direct weakening of the 
cardiac contractions. Such a direct effect upon the heart would 
not be unexpected, for, as I have mentioned, all venoms act as 
cardiac poisons when supplied to the excised heart of cold blooded 
vertebrates, 
Diminished peripheral resistance, owing to vaso-motor paresis, 
does no doubt contribute a share to this final fall in pressure, but 
that vaso-motor action is not altogether in abeyance, and may 
still be called into operation by sufficient stimulus is shown by 
the effect of asphyxiation on a curarised animal in which the 
Pressure has sunk to less than one-half its previous height. In 
®xperiments 14 and 15, the pressure was in both instances, under 
such circumstances, doubled by suspension of the artificial respir- 
en. In other experiments upon rabbits, as soon as the respir- 
ation showed signs of incipient failure, artificial inflation was 
employed. Directly this was discontinued, and the animal had 
to depend on its own inadequate respiratory movements for a 
“upply of oxygen the pressure rose at once. The only cause of 
ae : rise is that brought about by the vaso-motor mechanism. 
This is stil capable of about doubling the arterial pressure for 
