142 PHYTOTOXINS AND ZOOTOXINS 



The essential anatomical differences between the different classes of snakes are 

 as follows: Colubrickp, whicli include all the non-poisonous snakes, have no 

 mechanism for injecting poisons into their victims. Colubridce venenoscB are 

 venomous snakes resembling in many particulars the harmless Colubrines. but 

 having short poison fangs, firmly fastened to the maxilla in an erect position; 

 in this class are included the cobra and the venomous snakes of Australia. Vi- 

 peridce, or vipers, are characterized by a highly specialized apparatus for in- 

 jecting the poison; their poison fangs are very long, and the maxillary bone, to 

 which they are fastened, is so articulated that it rotates about a quarter of a 

 circle when the snake strikes, bringing the fangs into an erect position. The 

 fangs are canalized and pointed at the end like a hypodermic needle, and the 

 poison is forced through them under considerable pressure bj^ a large muscle that 

 contracts over the salivary gland. Accessory fangs in various stages of develop- 

 ment are also present to replace any fang lost in action. All the poisonous snakes 

 of Morth America, with one insignificant exception, belong to the vipers, and to 

 a special class known as the "pit vipers," because of the presence of a deep pit 

 of unknown function above the maxilla. The exception mentioned is the "coral 

 snake" found on the coast of Florida, around the Gulf of Mexico and in the south- 

 eastern states; it is a member of the colubrine poisonous snakes, of small size, and 

 seldom causes serious poisoning. The poisonous vipers are the rattlesnakes 

 (Crotahis), of which there are some ten to twelve or more species, and Sistrurus of 

 which there are two species ; the copperhead adder {Andstrodon coniroirix) and 

 the water mocassin {Andstrodon piscivorus). 



The classification used above is the one followed in most publications on 

 poisonous snakes; a more modern classification divides the snakes {Ophidia) into 

 several .series, one of these including all poisonous snakes under the title of Pro- 

 teroglypha, and dividing this series into the three families: (1) Elapimv, including 

 cobras, coral snakes, etc.; (2) Hydrophince, the poisonous sea-snakes; (3) Viperidce, 

 including all snakes with erectile fangs. -^ 



The source of the venom is probably in part the blood, since snake 

 blood has been found to contain poisons very similar to some of those 

 in the venom; therefore these are presumably simplj^ filtered out by 

 the venom glands, and not manufactured by them.^^ Other poison- 

 ous constituents of venom are not found in snake serum, and there- 

 fore are probably manufactured by the venom gland. Apparently 

 many of the harmless snakes produce a poisonous saliva, since extracts 

 of their glands are said by Blanchard^^ to possess the properties of the 

 venoms, and if so these snakes are harmless chiefly because they 

 lack an apparatus for injecting the poison. As a rule, however, the 

 venom glands are much more highly developed in the poisonous snakes, 

 and are connected with a specialized injection apparatus; in structure 

 they are compound racemose glands. 



Properties of Venom. — As ejected, the venom is weakly acid or 

 neutral in reaction, and free from bacteria, contrary to earlier ideas 

 (Langmann). Its specific gravity is 1030 to 1077, and it contains a 

 large amount of solids, generally 20 to 40 per cent, by weight. These 

 are precipitated by alcohol, ether, tannin, and iodin, but do not ad- 



^* For a full discussion of the characteristics of the poisonous snakes of North 

 America, see the monograph with that title by Stejneger, Report of U. S. Na- 

 tional IVIuseum, 1S<.).'{, Wasliingtou. A good summary is also given by Langmann, 

 Jlefcreiic(! Handbook of Medical Sciences, ('oiicerniiig })oisonous sca-snakos, 

 Ili/droplniliu, see Hoiilanger, Natural Science, 1S92 (1), 41. The poisonous snakes 

 of India are descril)ed by Fayrer, in "The Thanatopliidia of India," JiOndon, 1874. 



'^'' Contradicted by Arthus, Arch, internat. phvsiol, 1912 (12), 102. 



^» Com])t. Uend. Soc. Biol., 1894 (40), 35. 



