VACCINATION AGAINST SNAKE-VENOM 247 



their toxicity, aiul, if these be employed, the dose of venom 

 calcinated to kill the control animals in thirty minutes, for 

 example, takes an hour or more to do so. 



I always prepare ni}^ test solutions of venom in the following 

 manner : — 



Ten milligrammes of dry cobra-venom are weighed in a didicate 

 balance. The venom is dissolved in 10 c.c. of 0"8 per cent, physio- 

 logical salt solution, which takes a few minutes. When the venom 

 is thoroughly dissolved it is transferred to a test-tube, which is 

 immersed for three-quarters of an hour in a water-bath heated to 

 + 72^ C. In this way the non-toxic albumins are coagulated 

 without modifying the neurotoxic substance. The solution is 

 p3ured on to a filter of sterilised paper, and the clear liquid 

 which is collected is immediately put up in glass phial?, which 

 are hermetically sealed, or in small sterilised bottles. Its toxicity 

 is tested upon control animals, and it may be kept for five or 

 six days if protected from light, or for several weeks in a refrigerator 

 at about 0° C. 



One-tenth of this solution corresponds exactly to 1 milligramme 

 of dry venom. 



As for the antivenomous serum, as soon as its antitoxic value 

 has been ascertained by the methods that I have just described, and 

 it has been separated from clots and red corpuscles by suitable 

 decantation, it is portioned out, with the usual aseptic pre- 

 cautions, into small sterilised bottles of 10 c.c. capacity, without 

 the addition of any antiseptic. 



In order to ensure that it will keep for a long time, care is 

 then taken to heat the hermetically sealed bottles in a water-bath 

 at a temperature of 58° C. for one hour, and this operation is 

 repeated for three days in succession. 



Serum prepared in this way preserves its antitoxic power 

 unimpaired for about two years, in all climates. I have had 

 occasion at various times to receive bottles which had been sent 

 eighteen months and two years previously to India and Indo-China, 



