THE START 13 



pit-viper is wholly or well-nigh useless as regards the 

 colubrines. The animal that is immune to the bite of 

 one may not be immune to the bite of the other. The 

 bite of a cobra or other colubrine poisonous snake is more 

 painful in its immediate effects than is the bite of one 

 of the big vipers. The victim suffers more. There is a 

 greater effect on the nerve-centres, but less swelling of the 

 wound itself, and, whereas the blood of the rattlesnake's 

 victim coagulates, the blood of the victim of an elapine 

 snake — that is, of one of the only poisonous American col- 

 ubrines — ^becomes watery and incapable of coagulation. 



Snakes are highly specialized in every way, including 

 their prey. Some live exclusively on warm-blooded ani- 

 mals, on mammals, or birds. Some live exclusively on 

 batrachians, others only on lizards, a few only on insects. 

 A very few species live exclusively on other snakes. These 

 include one very formidable venomous snake, the Indian 

 hamadryad, or giant cobra, and several non-poisonous 

 snakes. In Africa I killed a small cobra which contained 

 within it a snake but a few inches shorter than itself; but, 

 as far as I could find out, snakes were not the habitual 

 diet of the African cobras. 



The poisonous snakes use their venom to kill their 

 victims, and also to kill any possible foe which they think 

 menaces them. Some of them are good-tempered, and 

 only fight if injured or seriously alarmed. Others are ex- 

 cessively irritable, and on rare occasions will even attack 

 of their own accord when entirely unprovoked and un- 

 threatened. 



On reaching Sao Paulo on our southward journey from 

 Rio to Montevideo, we drove out to the "Institute Serum- 



