io68^ VENOMS AND ANTIVENINS 



over their fangs, raising and lowering them at will, as may be observed when snakes yawn 

 and stretch their fangs. Introduction of venom is accomplished by the combined action of 

 several muscles which cause the opening of the mouth, the erection of the fangs, and the 

 compression of the glands, thereby forcing the venom through the duct and fangs at the same 

 instant that the snake strikes its victim. At the end of the stroke the fangs are withdrawn 

 from the site of the bite; the mouth closes as the fangs fold back; mechanical compression 

 constricts the duct, and pressure upon the gland is relieved by the relaxation of the involving 

 muscles. 



The hollow or grooved fang is firmly ankylosed to the maxillary bone, which is located 

 anteriorly on each side of the upper jaw. There is a pair of functional fangs which are supple- 

 mented by one or many more pairs of smaller ones which are not attached to the bone but lie 

 imbedded in the buccal tissues. When, from any cause, one of the larger fangs is broken off, 

 the reserve fang nearest to it moves into its place, adheres to the maxillary bone, and finally 

 becomes the functional poisoning fang. 



VENOM AMOUNTS 



The quantity of the poison secreted varies according to the species and, as a rule, is pro- 

 portional to the size of the snake, although there are exceptions to this rule: The Disteiri- 

 dae secrete very little poison in relation to their size; the Neotropic rattler secretes less and 

 less poison as it grows older, the individuals of medium age yielding the largest amounts. 

 Captivity also exerts a noticeable influence on the secreting activity of the poison glands, re- 

 tarding or even inhibiting it. In general, however, it may be said that the following is the 

 approximate amount in milligrams of dried poison produced by the medium-size examples of 

 a few species at a bite or obtained at a single extraction. 



a) North American species: Mg. 



Copperhead (A. mokasen) 45- 60 



Water moccasin {A. piscivorus) 90-150 



Timber rattler (C. horridus) 60- 90 



Texas rattler (C. atrox) 90-120 



Pacific rattler (C. oreganus) 60- 75 



. Bleached rattler (C mitchelUi) 70-120 



Red rattler (C. exsul) 60-120 



Florida rattler (C. adainanle:is) 240-350 



b) South and Central American species: 



Rattlesnake (C. terrificus) 30- 60 



Fer-de-lance {B. atrox) 100-180 



Jararacussu {B. jararaciissii) 200-330 



Bushmaster (L. mnta) 300-500 



c) Australian species: 



Tiger snake {N. curtus) 35-40 



d) Indian species: 



Cobra {N. naja) 250-350 



Daboia (Z>. russelUi) 200-300 



VENOM CHARACTERISTICS 



d) Specificity. — ^There seems to be some adaptation of the toxicity of venoms to 

 the species of animals on which snakes feed. Venom is one of the snake's digestive 

 juices, and I believe that some differentiation in their action on the tissues of the 



