Venoms are modified or destroyed by certain normal diastases of the organism. It was shown long ago by Lacerda, Weir Mitchell, Sir Joseph Fayrer, and Lauder Brunton, that it is possible to introduce without danger into the stomachs of adult animals amounts of venom many times greater than the lethal dose. I have repeatedly verified this, but have nevertheless observed that young mammals, while being suckled, readily absorb venom by their alimentary canal, and succumb to the ingestion of doses scarcely larger than those which kill when subcutaneously injected. Here we have a very important fact, which once more proves how easily the intestinal mucous membrane of young animals is permeated by toxins. By my instructions Wehrmann[64] and Carrière,[65] in my laboratory, have studied the modifications undergone by venoms in the alimentary canal of rabbits. We have seen that these animals can ingest without inconvenience doses of venom 600 times greater than the lethal dose, and that, if we cause these ingestions to be repeated several times, contrary to the assertion of Fraser[66] (of Edinburgh), we never succeed in obtaining immunity to the subcutaneous injection of a simple lethal dose, and no antitoxin is formed in the blood. The _ptyalin_ of the saliva, _pancreatic juice_, and _bile_ destroy _Cobra_-venom _in vitro_. We must, therefore, assume that these diastases are veritable agents of destruction for ingested venom. The intestinal microbes play no part, any more than the intestinal juice by itself. The gastric juice has very little effect. Papain is almost as active as the pancreatic juice. It had already been proved by Fraser, so long ago as 1895, that bile, after prolonged contact and in a sufficient dose, has a strongly destructive effect upon Cobra-venom; but, contrary to the opinion of this investigator, it is not antitoxic, for it possesses no preventive or curative property, and its effects are produced only _in vitro_. We see from what has been stated above, that venoms introduced into a sensitive organism are capable of producing extremely complex effects upon the various tissues or humours. They act on the nerve-cells by their _neurotoxin_, on the endothelium of the blood-vessels by their _hæmorrhagin_ (Flexner and Noguchi), on the red corpuscles by their _hæmolysin_, on the fibrin of the blood and muscles by their _proteolytic diastase_, and on the fibrin-ferment itself by their _thrombase_. They also act on the leucocytes, according to the experiments of Chatenay,[67] performed under the direction of Metschnikoff, and according to those of Flexner and Noguchi,[68] already cited. Thus we understand how complex must likewise be the means of defence that have to be employed in order to afford an effective protection against such poisons.