PHYSIOLOGICAL ACTION OF VENOM OF BLACK SNAKE. 177 
It would thus appear that the establishment of a negative 
variation confers an immunity, as far as intravascular clotting is 
concerned, against further injections of the venom. This immunity 
is very speedily produced ; how long it may last I am at present 
not in a position to say. 
These facts explain how it is that one can introduce large 
quantities of the venom into the circulation, provided this be done 
slowly, without producing intravascular clotting. The first portion 
of the injection causes a transitory positive phase, 7.¢., increased 
coagulability, but not sufficient to cause actual thrombosis. This 
is immediately superseded by a negative phase and the establish- 
ment of this inhibitory phase confers immunity against the 
remainder of the injection. 
Before discussing the bearings of these facts, I shall indicate 
the results of an examination of shed blood which has been sub- 
jected to the action of the venom, and of some of the reactions of 
the non-coagulable blood, itself. 
Action of a solution of venom on the coagulation of shed blood. 
To determine whether a solution of venom were capable of 
exerting any influence upon shed blood, I dissected out three 
inches of the femoral artery of a dog, and bled from this directly 
into a solution of the poison. The cut end of the artery was 
immersed in a ‘9% solution of NaCl, containing 0°1% of venom. 
’ By relaxing the compression of the fingers, a small amount of 
| blood—equal to the volume of the salt solution—was allowed to 
flow into the vessel. The two fluids were at the same time freely 
mixed by agitating the end of the artery. The blood began to 
thicken in fifty-six seconds, but clotting did not proceed in a 
‘ormal manner. At the end of an hour, a small soft clot formed, 
which on shrinking failed to entangle all the corpuscles. The 
Vessels containing the mixture of blood and venom solution could 
at no time be inverted without upsetting the contents, as could 
be done to the vessel in a control experiment with salt solution 
L—July 3, 1995, 
