PHYSIOLOGICAL ACTION OF VENOM OF BLACK SNAKE. 175 
dogs which had had a meal three hours previously were used, 
whereas the last four experiments were made upon animals which 
had fasted for nearly twenty-four hours. 
(3) Influence of Rapidity of Injection. 
The variations in effect caused by alterations in the rapidity of 
injection are very marked. So much so, that it is impossible to 
compare the results from different experiments, unless the rate 
with which the poison is introduced is a constant factor. Intra- 
vascular clotting is produced most readily if the dose be rapidly 
thrown into a vein near the heart (e.g. the jugular). On increas- 
ing the time of delivery of the poison into the circulation, either 
by employing diluted solutions, or by pressing down the piston of 
the syringe more slowly, the positive phase (increased coagulability 
of the blood), is less and less pronounced. Tf the duration of the 
injection be still further prolonged, the positive phase, if present, 
is so rapidly succeeded by the negative variation that this latter 
appears to be the only result. . The negative phase becomes more 
and more pronounced as larger quantities of the venom are allowed 
to slowly enter the circulation. For slow injections I have con- 
nected a burette containing a very dilute solution of venom in 
_ ‘TY, NaCl with the cannula in the vein, by a piece of rubber tube, 
the calibre of which was controlled by a screw clamp. With this 
arrangement I have been able to introduce large doses (0 005 
gramme per kilo.), without producing intravascular clotting. 
The discovery that the effects on the blood plasma after slow 
: injections, are vastly different from, in fact exactly opposite to, 
: those following rapid introduction of the venom, explains why, in 
‘My earliest experiments, I did not obtain the same fluid condition 
_ Of the blood as Halford,! who used either subcutaneous injection 
of the venom, or else allowed a snake to bite the dog. By these 
methods delivery into the circulation would necessarily be slow, 
~ comparable with results obtained by intravenous injection 
only in cases in which such injection was very gradually 
1 Loc. cit. 
