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CHAPTER XI. 
NATURAL IMMUNITY OF CERTAIN ANIMALS WITH 
RESPECT TO SNAKE-VENOMS. 
Ir was long ago pointed out that certain warm-blooded animals, 
including the mongoose (Herpestes ichneumon, Family Viverridæ), 
hedgehog (Hrinaceus europeus, Family Erinaceide), pig (Sus 
scrofa, Family Suidæ), and some herons (Ajaja, Subfamily Plata- 
leine; Cancroma, Subfamily Cancromine : Botaurus, Subfamily 
Ardeine : Mycteria, Subfamily Ciconiinæ), known in Colombia 
under the names Culebrero and Guacabo, 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 Cobra-venom (10 milligrammes) 
capable of killing a large-sized dog. The animal withstood the 
injection, but I am inclined to think that this is not a case of true 
immunity ; it 1s probable that the pig owes its resistance to venom 
to the fact that its skin is ined 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 Cobra-venom, lethal for 
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 
