By degrees the drowsiness and the difficulty of breathing become greater; the pulse, which at first is more rapid, becomes slower and gradually weaker, the mouth contracts, and there is profuse salivation, the tongue appears swollen, the eyelids remain drooping, and, after a few hiccoughs frequently accompanied by vomiting and involuntary emissions of urine or fæcal matter, the unfortunate victim falls into the most profound coma and dies. The pupils react to luminous impressions up to the last moment, and the heart continues to beat sometimes for two hours after respiration has ceased. All this takes but a few hours, most frequently from two to six or seven, rarely more. When the reptile by which the bite is inflicted is one of the _Solenoglypha_, such as a _Lachesis_ for example, the seat of the bite immediately becomes very painful and red, then purple. The surrounding tissues are soon infiltrated with sanguinolent serosity. Sharp pains, accompanied by attacks of cramp, extend towards the base of the limb. The patient complains of intense thirst, and extreme dryness of the mouth and throat; the mucous membranes of the eyes, mouth, and genitalia become congested. These phenomena often continue for a very long period, even for more than twenty-four hours, and are sometimes accompanied by hæmorrhages from the eyes, mouth, stomach, intestines, or bladder, and by more or less violent delirium. If the quantity of venom absorbed be sufficient to cause death, the patient exhibits, a few hours after being bitten, stupor, insensibility, and then somnolence, with increasing difficulty of respiration, which ends by becoming stertorous. Loss of consciousness seems complete a good while before coma appears. Asphyxia then ensues, and the heart continues to beat for nearly a quarter of an hour after respiratory movements have entirely ceased. In certain exceptional cases death is very rapid; it may supervene suddenly in a few minutes, even before the local phenomena have had time to manifest themselves; in this case the venom, having penetrated directly into a vein, has produced almost immediate coagulation of the blood, thus causing the formation of a generalized embolism. If the venom be introduced in a highly vascular region, or directly into a vein, the result is almost invariably fatal. On the contrary, if the derm be scarcely broken, or if the clothing has acted as a protection, scarcely any absorption will take place. We are here confronted with the same factors of gravity as in the case of bites inflicted upon human beings by animals suffering from _rabies_. In experiments we are able to eliminate all these factors, and to follow in an animal inoculated with a known quantity of venom the whole series of phenomena of poisoning, the intensity of which can be graduated. Let us see, then, how the various animals that it is possible to make use of in laboratories behave with regard to venoms of different origins.