I then took blood from three other mongooses, by tying a carotid without killing the animals. This blood, mixed with venom or injected as a prophylactic into rabbits, exhibited an antitoxic power, which, though evident, was of little intensity, and insufficient in all cases as a certain preventative of death. All the rabbits that received a preventive dose varying from 2 to 7 c.c. of mongoose-serum succumbed to inoculation with venom, but with a considerable retardation (from two to five hours) as compared with the controls. I endeavoured to determine the limit of tolerance of the mongoose with respect to venom. Two of these animals, which had never been inoculated, received doses of venom respectively four times and six times lethal for the rabbit. The first mongoose remained perfectly well; the second was ill for two days, and then recovered. A third mongoose, into which I injected a dose eight times lethal for the rabbit, succumbed in twelve hours. [Illustration: FIG. 89.--MONGOOSE SEIZED BY A COBRA. (For this illustration I am indebted to the kindness of M. Claine, late French Consul at Rangoon.)] It must be concluded from these facts that the West Indian mongoose is but little sensitive to venom; that it is capable of withstanding, without malaise, doses which are considerable in proportion to its size, but that its immunity is far from being absolute. If it is generally the victor in its combats with poisonous snakes, the result is mainly due to the extreme agility with which it is endowed. A number of experiments have been made by Lewin,[84] and by Phisalix and Bertrand,[85] upon the immunity of the hedgehog to the venom of _Vipera berus_. It had long been known that hedgehogs are inveterate hunters of vipers, which they devour with avidity. Thanks to the long and sharp spines by which their bodies are protected, they avoid being bitten and contrive to catch the reptiles very cleverly, but it occasionally happens that they do not escape being struck. However, even in these cases they rarely succumb. Inoculation with fairly large quantities of venom does not make them ill: the dose of _viper_-venom lethal for these small animals is about forty times greater than that which kills the guinea-pig. Their power of resistance is therefore beyond doubt. It may be asked whether this is due to their blood normally containing antitoxic substances. In order to elucidate this question, Phisalix and Bertrand first proved that the blood of normal hedgehogs is toxic to laboratory animals, especially to the guinea-pig. A mixture of this blood with viper-venom cannot therefore be harmless. But it sufficed to heat hedgehog blood to 58° C. to cause it to lose its toxicity, and it was found that it then became antitoxic. Guinea-pigs inoculated in the peritoneum with 8 c.c. of heated hedgehog-serum were able to withstand, immediately afterwards, twice the lethal dose of viper-venom.