176 VENOMS 
The lethal dose for a horse being, as I have ascertained by my 
own experiments, about 0°025 gramme, 1 gramme of dry Cobra- 
venom will therefore suffice to kill 20,000 kilogrammes of horse. 
Assuming 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 0°015 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 Lachesis 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. 
