"The following table gives the relative toxicity, for 1 kilogr. of rabbit, of the different venoms that I have tested. To denote this toxicity I use terms such as Behring, Roux, and Vaillard used for the toxin of tetanus, taking the number of grammes of animal killed by one gramme of toxin:-- 1. Venom of _naja_ 0.25 mgr. per kilogr. of rabbit. One gramme of this venom kills 4000 kilogrammes of rabbit; it has, therefore, an activity of 4,000,000 2. Venom of _hoplocephalus_ 0.29 mgr 3,450,000 3. Venom of _pseudechis_ 1.25 mgr 800,000 4. Venom of _pelias berus_ 4.00 mgr 250,000 "Of course, this estimation of virulence is not absolute; it varies considerably according to the species of animal tested. Thus the guinea-pig, and still more the rat, are extremely sensitive. For instance, 0.15 mgr. of viper-venom is enough to kill, in less than 12 hours, 500 grammes of guinea-pig; so that the activity of this venom with a guinea-pig is 3,333,000, but with a rabbit is not more than 650,000. With more resistant animals, the opposite result is obtained; about 10 mgr. of cobra-venom are necessary to kill a dog of 6.50 kilogrm. weight; but to kill the same weight of rabbit 1.65 mgr. is enough. Thus the virulence of this venom with the rabbit is 4,000,000; but with the dog not more than 650,000." By experiments in test-tubes, Calmette studied these venoms under the influences of heat and various chemical agents. He found how to attenuate their virulence, and how to diminish the local inflammation round the point of inoculation; and it was in the course of these test-tube experiments and inoculations that he discovered the value of calcium hypochlorite as a local application. Working, by various methods, with attenuated venoms, he was able to immunise animals:-- "I have come to immunise rabbits against quantities of venom that are truly colossal. I have got several, vaccinated more than a year ago, which take, without the least discomfort, so much as 40 mgr. of venom of _naja tripudians_ at a single injection; that is to say, enough to kill 80 rabbits of 2 kilogr. weight, or 5 dogs. "Five drops of serum from these rabbits wholly neutralise _in vitro_ (in a glass test-tube) the toxicity of 1 mgr. of _naja_-venom." By 1894 he had found that the serum of an animal, thus immunised by graduated doses of one kind of venom, neutralised other kinds of venom:--