56 THE VENOM OF HELODERMA. 



venom contained large numbers of bacteria, some of which proved to be ex- 

 tremely virulent for guinea-pigs.* In making use of sublethal doses and of 

 doses which kill only after a considerable interval, it was of course necessary to 

 eliminate the influence of micro-organisms. Almost all our experiments have 

 been made with venom sterilized either by boiling for 10 minutes or by being 

 kept for an hour at a temperature of 60. The advantage of the latter method 

 is that the resulting precipitate is a much finer one and passes easily through 

 a fine hypodermic-syringe needle. 



A large number of tests were made comparing the toxicity of heated and 

 unheated venom. The toxicity of the venom was tested in guinea-pigs, rats, 

 rabbits, mice, and tadpoles. The venom used in these experiments had been 

 heated either to 60 C. for an hour, 100 C. for 10 minutes or 30 minutes, or to 

 120 C. in the autoclave for 15 minutes. The injection of any of the heated 

 venoms led to the death of the animals almost as quickly as the injection of 

 unheated venom. 



Thus it was apparent that heat of such degrees as we have used in these 

 experiments does not injure the toxicity of the fresh venom to any marked 

 degree. However, it was noted occasionally that when animals were injected 

 with small quantities of the heated venom (that is, quantities which were but 

 very little larger than the lethal dose), such animals lived longer after the injec- 

 tion than animals injected with corresponding quantities of the unheated 

 venom. Therefore it appears that the heating exerts some slight injurious 

 effect on the venom. This slight decrease in the toxicity after heating may 

 perhaps be due to an inclusion of some venom in the coagulum. It will pre- 

 sumably require some time for the included venom to be liberated; the action 

 of the venom is, therefore, distributed over a longer period of time and is con- 

 sequently less acute. 



With dried venom we tested the influence of exposure to temperature of 

 80 C. for 1 hour, 100 C. for 1 hour, 120 C. (autoclave) for both 1 and 2 hours. 

 In these experiments only mice were used. It was found that the heating of 

 the dissolved dry venom did not diminish its toxicity, although in a few cases it 

 was observed that animals injected with the smaller doses of the heated venom 

 did not die quite as soon as animals injected with the same quantities of un- 

 heated venom. Santesson records the fact that the dried venom would not 

 endure heating to 110C, while the fresh venom would. The reason for this 

 difference between Santesson's observations and ours is not clear. 



The action of heat upon various snake venoms differs; thus, the venom of 

 Colubridse (Naja, Bungarus, Holocephalus, and Pseudechis) and of Hydrophinee 

 may be heated to 100 C. and even boiled for a short time without injury; heat- 

 ing for a long time to 100 C. or heating to 120 C. diminishes or destroys the 

 toxicity. The venom of Viperidse (Lachesis, Crotalus, Viperd) is injured by 

 being heated to 70 C. and is destroyed at 80 to 85 C. 



Unlike the heloderma venom, the venom of the Colubridae gives a pre- 

 cipitate which appears after heating to 72 C. and which is not toxic. 



*Bacteria belonging to the group of the colon were especially virulent, as found by Dr. D. Rivas. 



