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CHAPTER XL 



NATURAL IMMUNITY OF CERTAIN ANIMALS WITH 

 RESPECT TO SNAKE-VENOMS. 



It was long ago pointed out that certain warm-blooded animals, 

 including the mongoose {Herijestes ichneumon, Family Viverridce) , 

 hedgehog (Erinaceus europcBus, Family ErinaceidcB), pig {Sus 

 scrofa, Family Siiida), and some herons {Ajaja, Subfamily Plata- 

 leincB ; Cancroma, Subfamily Cancromina : Botaunis, Subfamily 

 ArdeincB : Mijcteria, Subfamily Cico7iiinai), known in Colombia 

 under the names Gulehrero and Gtiacabo, exhibit a natural immunity 

 with respect to snake-bites. 



Pigs devour vipers with great readiness, and in the region of 

 North America which adjoins the Mississippi and its tributaries 

 they are even trained to destroy the young rattle-snakes and other 

 poisonous serpents with which the valleys of these watercourses 

 are infested. 



During my stay in Indo-China I inoculated a young pig, beneath 

 the skin of the back, with a dose of Cohm-\enom. (10 milligrammes) 

 capable of killing a large-sized dog. The animal withstood the 

 injection, but I am inclined to thmk that this is not a case of true 

 immunity ; it is probable that the pig owes its resistance to venom 

 to the fact that its skin is lined with an enormous layer of adipose 

 tissue, which is but very slightly vascular, and in which absorption 

 takes place very slowly. This opinion is corroborated by my dis- 

 covery that the serum of this animal is entirely destitute of any 

 antitoxic substance. I mixed a dose of Co^ra-venom, lethal lor 

 the rabbit, with 3'5 and 8 c.c. of pig-serum. These mixtures killed 

 rabbits in the same time as the controls that received the venom 



