VENOM OF SNAKES. 117 



I give here Calmette's table concerning the toxicity of dry 

 venom : — 



One gramme of dry cobra's venom kills approximately* — 

 1 ,250 kilogrammes of dog. 



Although cold has no action on the toxic properties of liquid 

 venoms, heat coagulates and modifies their chemical composition. 

 The action is different on Hquids obtained from Colubridse from 

 those obtained from Viperidse. According to Calmette, in the first 

 case (Colubridse) venoms retain their toxicity with temperature of 

 about 100° C. ; this toxicity is completely destroyed at 120° C. only. 

 In the second case (Viperidae) toxicity disappears betAveen 65° C. 

 and 85° C. Therefore it is not possible to give a general rule as to 

 the resistance of venoms against heat, especially as there are large 

 differences in this resistance between closely related species of the 

 same genus. 



Venom presents most of the chemical reactions which characterize 

 proteic matter, viz., precipitation by absolute alcohol ; reaction of 

 biuret ; xantho-proteic reaction ; precipitation by picric acid, with 

 disappearance of the precipitate by heating, &c. 



Such, in brief, are some of the most important physical and 

 chemical properties of venom. Concerning the physiological 

 properties, I will indicate only their two chief functions. It must 

 be borne in mind that if venoms are an offensive and defensive 

 secretion, they are also an indispensable secretion for the digestion 

 of aliments. In fact , the non-venomous snakes {Tropidonotus natrix) 

 possess parotid and supra-labial glands which secrete venomous 

 saliva (works of Leydig, Reichel, Blanchard, Physalix, Bertrand, 

 &c.), but they are deprived of the special channelled teeth which 

 enable venomous snakes to inoculate their poison. 



Symptoms resulting from the biting of Venomous Snakes. 



Calmette has proved that all venoms contain at the same time a 

 neurotoxin and a hemorragin, but in various proportions. That in 

 Colubriclge and Hydrophidse, neurotoxin predominates, whereas with 

 Viperidse there is predominance of hemorragin. Therefore, in case 



* The toxicity of venom varies a great deal according to the physiological 

 state of the animal ; it is much greater (about ten times) after the moulting or 

 after a long fast. 



