220 TROPICAL MEDICINE AND HYGIENE 



constituents of venom in the same way as they can be 

 immunized to bacterial toxins, and that the blood-serum 

 of the immunized animals develops antagonistic bodies, 

 or antivenoms, comparable with the bacterial antitoxins 

 of modern therapeutics. We have, moreover, consider- 

 able experimental evidence that just as the various 

 bacterial antitoxins are specific, so also these antivenoms 

 are specific, that is to say, any given antivenom is 

 antagonistic only to the venom of the particular species 

 of snake that elicits it. This well-grounded belief in the 

 specific limitations of antivenoms makes it incumbent on 

 every medical man, who hopes to follow 'the modern 

 treatment of snake-bite by antivenomous sera in a 

 rational manner, to know something more than how 

 merely to recognize a venomous snake as such. He must 

 be able to distinguish species ; and to this end it is 

 advisable for him to understand how and upon what 

 structural characters snakes are classified, and to appre- 

 ciate the value of specific criteria ; and his work will be 

 made easier if he also knows what genera and species 

 he may expect to find in any particular locality. 



i. GENERAL ZOOLOGICAL CHARACTERS AND 

 CLASSIFICATION OF SNAKES. 



The Snakes (Ophidia) form an Order of the Class of 

 Reptiles, and are distinguished by their elongate, limbless 

 body covered by horny epidermal scales, by their wonder- 

 fully flexible mouth, by the absence of eyelids and of 

 a tympanic cavity and external ear-opening, and by 

 having the cloacal orifice transverse, and the penis paired. 

 The extraordinary [distensibility of the mouth is due 

 partly to the length and mobility of the quadrate bone 

 (q., fig. 95), from which the jaws and bony palate are 

 suspended, partly to the looseness of the attachment 

 of the individual bones of the upper jaw 7 and palate, 

 and very largely to the fact that the rami of the lower 

 jaw are loosely held together by an elastic symphyseal 



