REPTILES IN CAPTIVITY 195 
covered with a green leaf, and places this green leaf immedi- 
ately in front of the serpent’s mouth. By pressing the back 
of the animal's neck with the fingers it can be made to open 
its jaws and bite deeply into the leaf. When killing their 
prey snakes use only a small portion of the poison which 
their fangs contain, but when subjected to pressure in the 
manner above described, they eject their whole supply, which, 
passing through the holes in the leaf made by the bite, collects 
in the hollow of the mussel shell beneath. By the employment 
of this method it has been found that the collected poison of 
_ a hundred cobras in the dried state amounts to no more than 
four grammes. This would be sufficient to kill several hundred 
large mammals or several thousand men—so concentrated 
and so virulent is the poison. A reptile which has been 
deprived of its poison in this manner takes about a week 
to renew its supply. 
Mr. Docton also made experiments as to the practicability 
of conferring immunity from the effects of snake poison by 
administering small but gradually increasing injections of the 
liquid. On this point he completely established his case. 
It was found possible to render monkeys immune within a 
period of six months ; and, taking into consideration the well- 
known similarity between the reactions of monkeys and men, 
there seems no reason to doubt that a similar immunity might 
easily be conferred upon human beings. It has not yet been 
ascertained whether immunity from the poison of one species 
of snake would carry with it immunity from the poisons of all 
other species; but any such general immunity appears im- 
probable, and for the following reason. When two snakes 
of the same species attack one another they remain unaffected 
by each other’s poison, but when the reptiles are of different 
species they rapidly succumb to each other's bites. This 
statement, which I make on the authority of Mr. Docton 
and which I firmly believe to be true, seems to indicate a 
great difference in the quality of the poisons of the different 
species. The dried snake poison is of a yellowish-green 
13* 
