50 EXPERIMENTS WITH POISONOUS SNAKES, 



should one be bitten by another of the same species, 

 little or no ill effect ensues. 



In confirmation of this, I have heard, on good 

 authority, that several puff-adders, confined in a 

 large box together, used to bite each other furiously 

 whenever irritated, and none of them ever died of 

 the results. Of course this does not apply to 

 serpents of a different kind, as I have seen the 

 American water viper kill a common English snake 

 placed in the same case. In this instance the 

 poison was some time in taking effect, as the snake 

 writhed about for a long time, being bitten on the 

 back of the neck. Even after an hour or two had 

 elapsed a considerable degree of muscular irritability 

 remained. 



Our first experiment was tried with an Egyptian 

 cerastes. This snake is remarkable for having 

 above the eyes two small upright scales resembling 

 horns, which peculiarity, together with the vertical 

 pupils peculiar to the eyes of nearly all the 

 poisonous species, gives it a far from engaging 

 aspect. In this serpent we find a good example of 

 how the colours of the reptilia are adapted to the 

 localities they inhabit, with the view of rendering 

 them less distinctly visible to their prey. Thus the 

 scales of the cerastes, which lies half-buried among 

 sand and dry soil, are of a reddish tint, while the 

 vivid green of the beautiful tree-snakes is no less 



