436 DISEASES DUE TO VENOMS AND POISONS 



In striking liie body is coiled, the tail projecting, the head and 

 neck raised a few inches, the tongue darts to and fro, air passes forcibly 

 through the narrow glottis, causing hissing, the muscles contract, the 

 snake straightens, the head suddenly darts forwards and upwards as 

 required, the thrust being one-third to one-half of its body length. 

 The jaws are widely separated, the head bent back, the superior 

 maxillary bone is rotated forwards upon its lachrymal articulation, and 

 thus erects the fangs. The jaws are approximated, the fangs enter 

 the victim, the head is drawn violently backwards, and the teeth are 

 driven deeply into the flesh. Tlie lower jaw presses upwards and so 

 squeezes fluid from the gland along the duct, and injects the venom 

 forcibly into the wound at the same time as it is being enlarged. In 

 disentangling itself the fang may be lost, but this is of little moment 

 as others soon arrive. Unless the fangs become erectile no Avound is 

 made and the venom will flow upon the skin, doing no harm. 



U is very doubtful if any snakes " spit " venom. The amount that 

 can be injected varies with the species of reptile; its previous condition 

 of full or impaired nutrition; its nearness to the moulting period; and 

 according to the pressure applied to the gland. 



Also by captivity, interference of clothing, failure of the snake to 

 close its jaws, deficient elevation of the fangs, malapposition of the 

 orifices of the poison duct and the fang, and the rapid movement of 

 the victim attacked, thus shaking off the snake before it had time to 

 shut its jaws. 



Sea snakes inject but a few drops of venom which are very deadly. 

 The Indian cobra can inject i drachm. Snakes in captivity always 

 yield less venom. The Naja haje can produce about 0*36 grm. of 

 liquid in 100 days, i grm. of which yields about 0*336 grm. of 

 dry venom. 



Acton and Knowles have done some excellent work on this subject 

 in India. In their results their unit is as far as possible expressed in 

 milligrammes of desiccated venom. The yield of venom was ascer- 

 tained to be for the — 



The minimum lethal dose for man was estimated ingeniously. 

 They took the common cobra bite and studied all cases from classical 

 writers of fatal bites, from the study of which they concluded that 

 I3"6 mgm. would just fail to kill a man, hence 15 mgm. would just be 

 fatal. 



