But the effect of the venom of the poisonous colubrine snakes is totally different from, although to the full as deadly as, the effect of the poison of the rattlesnake or jararaca.  The serum that is an antidote 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 colubrines—­ becomes watery and incapable of coagulation.

Snakes are highly specialized in every way, including their prey.  Some live exclusively on warm-blooded animals, 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 excessively irritable, and on rare occasions will even attack of their own accord when entirely unprovoked and unthreatened.

On reaching Sao Paulo on our southward journey from Rio to Montevideo, we drove out to the “Instituto Serumtherapico,” designed for the study of the effects of the venom of poisonous Brazilian snakes.  Its director is Doctor Vital Brazil, who has performed a most extraordinary work and whose experiments and investigations are not only of the utmost value to Brazil but will ultimately be recognized as of the utmost value for humanity at large.  I know of no institution of similar kind anywhere.  It has a fine modern building, with all the best appliances, in which experiments are carried on with all kinds of serpents, living and dead, with the object of discovering all the properties of their several kinds of venom, and of developing various anti-venom serums which nullify the effects of the different venoms.  Every effort is made to teach the people at large by practical demonstration in the open field the lessons thus learned in the laboratory.  One notable result has been the diminution in the mortality from snake-bites in the province of Sao Paulo.