CHAPTER XXVII. 
NATURAL IMMUNITY. 
EFFECTS OF VENOM UPON SNAKES. 
The experimental data bearing on this question are more or less conflicting, 
but one fact has been established beyond any doubt, namely, that venomous 
snakes are not absolutely immune to the action of their own and alien venoms, 
though their susceptibility — subject to more or less fluctuation — is far less 
than that of the majority of innocuous snakes and saurians. The deter- 
minations of the effects of venom were carried out in two ways: one allowing 
the snake to bite either itself or other snakes; the other (which is more 
accurate and reliable) injecting the venom into the subject on which its effects 
were to be tested. 
Fontana‘ in his biting experiments failed to produce death on vipers by 
the bite of the same species. Claude Bernard? has, however, found that 
vipers succumb to the bite of vipers within 3 days. 
In 1861 Weir Mitchell made a series of experiments as to the effect of 
crotalus bite on the same species. His experiments are somewhat unique in 
their arrangement, as he tested the action of this venom upon the same snake 
from which it was taken, or by letting a snake bite itself at a spot denuded of its 
skin. In the biting method he obtained 3 positive results out of 4 experi- 
ments. In two of these cases death occurred in 1o days, and in another it 
took place in 14 days. By the injection method all three rattlers succumbed 
to their own venom. ‘The first, receiving 10 drops of its fresh venom, died in 
36 hours; the second, receiving 8 drops, died in 67 hours; the last was killed in 
7 days with 7 drops of its venom injected. The autopsies showed softening 
of the sites of the bite or injection, but not much alteration could be ob- 
served in the internal organs. Mitchell quotes the self-biting experiments 
made by Burnett on Crotalus, in which death usually followed the bite in a 
few minutes! 
Russell, Fayrer,? and Waddell,‘ working on the Indian venomous snakes, 
have obtained more negative results. In the majority of cases the snakes 
remained almost unaffected, or at least survived a large quantity of their own 
or alien venoms introduced either by the biting or by the injection methods. 
There are, however, a few instances where a venomous snake was killed by 
another species of venomous snake within a few days after the bite. Fayrer 
studied Cobra, Bungarus, Echis, and Daboia in this regard. Waddell, like 
Russell, obtained negative results. 

‘Fontana. Abhandlung iiber das Viperngift, 1787, Berlin. 
? Claude Bernard. Lecons sur l’effet des substances toxiques, 1857. 
3 Fayrer. The Thanatophidia of India. 1874. 
‘Waddell. Are venomous snakes antitoxic? An inquiry into the effect ‘of serpents’ venom upon the 
serpents themselves. Sci. Mem. Off. Arm. India, 1889, IV, 47. 
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