The slightly intoxicated organism at first reacts by the intervention of the leucocytes; a _hyperleucocytosis_ is produced, accompanied by a more or less considerable rise of temperature. After a few hours everything returns to its normal condition, and if the injection of a lethal dose of venom is repeated several times, at intervals of a few days, it is not long before antitoxic substances are found to appear in the serum. When the dose of venom injected is sufficient to cause death, we observe, a very few moments after the injection, a _lowering of temperature_ and a _hypoleucocytosis_, which is the more pronounced in proportion to the nearness of the dose of venom to the minimal lethal dose. With very strong doses the hypoleucocytosis has not time to manifest itself. It is therefore probable that, in intoxication by venoms as in that by the toxins of micro-organisms, the protective _rôle_ of the leucocytes is all-important, not only because these cells are capable of digesting venoms owing to their protoplasmic digestive juices, but also because they constitute if not the only, at any rate the principal source of the _antitoxic substances_ or _amboceptors_. CHAPTER X. _TOXICITY OF THE BLOOD OF VENOMOUS SNAKES._ Several physiologists, among whom it is right to mention Fontana,[69] Leydig,[70] Reichel,[71] Raphael Blanchard,[72] Phisalix and Bertrand,[73] and S. Jourdain,[74] have pointed out the presence of poison-glands in _Tropidonotus natrix_ or other non-venomous snakes, and have explained the immunity enjoyed by these animals with regard to venom as being due to the existence of an internal secretion of this poison. We also know, from the writings of Phisalix and Bertrand, that the blood of the viper, and that of the salamander and toad are toxic. For my part I have found[75] that the blood of _Naja_, _Bungarus_, _Lachesis_, and _Cerastes_ possesses the same properties, and a comparative study has been made by Wehrmann,[76] in my laboratory, of the toxicity of the blood of the viper and of that of the blood of the eel, already established by Mosso (of Turin).[77] It is remarkable to find that the blood of the various venomous or non-venomous snakes, like that of certain fishes, such as eels, produces, when injected beneath the skin or into the peritoneum, local and general effects very similar to those of venoms. Injections of 0·5 c.c. to 1 c.c. of the blood of the viper or of the common snake, beneath the skin of the guinea-pig, provoke an intense local reaction, which always results in the formation of an eschar. The injection of slightly stronger doses, 1 c.c. to 2 c.c., into the peritoneum, almost always kills these animals, like venom, with symptoms of respiratory asphyxia. The blood of _Naja tripudians_, injected subcutaneously, is lethal to the mouse in a dose of 0·25 c.c.