THE RATTLESNAKE 147 



to be non-venomous, it has of late years been found 

 out that there may be poisonous Hzards. In Central 

 America there is a rather large lizard known as Heloderma, 

 many of the teeth of which are grooved, and supplied 

 from large spittle glands. One of these creatures was 

 so ungrateful as to bite the hand of that distinguished 

 American naturalist. Dr. Shufeldt. Although he at once 

 sucked a considerable amount of blood out of the wound, 

 yet he soon felt very severe shooting pains up his arm 

 and down the same side of his body. The parts also 

 rapidly swelled, and he became so faint that he fell. 

 In two days, however, he recovered. Some of the saliva 

 of this lizard injected into a pigeon killed it in seven 

 minutes; and a rabbit, into the carotid artery of which 

 some had been impelled, died in less than two minutes. 

 It is said to aflfect the nervous system, including that of 

 the heart. 



But though this lizard resembles some serpents in 

 having grooved teeth, nevertheless these teeth and its 

 poison glands are situated in the lower jaw, whereas, as in 

 all serpents (save one, quite recently discovered), it is 

 only the teeth of the upper jaw which are grooved and 

 become " poison fangs." 



The structure of this venomous lizard shows us unmis- 

 takably that its poison fangs and those of serpents must 

 have arisen independently, and poison fangs must have 

 had a still more multiple origin, since those of the pit 

 vipers and those of the cobras must have also had an 

 independent origin, because their structural conditions 

 are so diverse and the groups to which these different 

 snakes pertain are so distinct. But such being the case, 

 it is not impossible that the fangs of poisonous tree- 

 snakes and poisonous water-snakes also had an inde- 

 pendent origin. 



