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 10 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, Bungarns, Echis, and Daboia in this regard. Waddell, like 

 Russell, obtained negative results. 



1 Fontana. Abhandlung iiber das Viperngift, 1787, Berlin. 

 ^ Claude Bernard. Legons sur I'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. 



264 



