176 VENOMS 



The lethal dose for a horse being, as I have ascertained by my 

 own experiments, about 0'0"25 gramme, 1 gramme of dry Cobra- 

 venom will therefore suffice to kill 20,000 kilogrammes of horse. 



Assummg that man, in proportion to his weight, possesses 

 a resistance intermediate between that of the dog and that of the 

 horse, we may consider that the lethal dose for a human being is 

 .about O'OIS gramme. It follows, therefore, that 1 gramme of venom 

 would kill 10,000 kilogrammes of man, or, let us say, 165 persons of 

 an average weight of 60 kilogrammes. 



Another extremely important fact, which must not be lost sight 

 of, is that differences of toxicity, which are often considerable, are 

 exhibited by the venoms of different specimens of the same species 

 of snake, or by the venom of the same snake collected at different 

 times. I have found, for instance, in the case of the specimens 

 of Naja and LacJiesis reared in my laboratory, that, according to 

 the length of time that the animals had been without food, and 

 to the nearness or otherwise of the moulting period, the venom 

 was more or less active, and that on evaporation it left behind 

 a more or less considerable quantity of dry extract. In certain 

 cases, immediately after the moult and after a prolonged fast, the 

 venom was ten times more active than after a plentiful meal or 

 before the moult. 



The figures given above must therefore not be regarded as 

 determining the minimal lethal doses of the different venoms, 

 except in a purely comparative way, and they must be considered 

 only as data useful to know when it is desired to experiment upon 

 animals with these substances. 



Variations of this kind are observed in the case of all species 

 of snakes. Thus Phisalix rightly insists upon the necessity of 

 always noting, besides the species of snake, the place of origin and 

 the season ; for he has himself seen that, as regards French vipers, 

 those of the Jura, for example, produce in the spring a venom 

 almost devoid of local phlogogenic action ; while vipers from the 

 vicinity of Clermont-Ferrand, though less toxic, produce much 

 more serious local effects. 



