The bite of all the Proteroglyphous Colubrids, even of the smallest and gentlest, such as the _Elaps_ or Coral-snakes, is, so far as known, deadly to man. The Viperidæ differ much among themselves in the toxicity of their venom. Some, such as the Indian _Vipera russelli_ and _Echis carinatus_, the American _Ancistrodon_, _Crotalus_, _Lachesis mutus_ and _lanceolatus_, the African _Causus_, _Bitis_, and _Cerastes_, cause fatal results unless a remedy be speedily applied. On the other hand, the Indian and Malay _Lachesis_ seldom cause the death of man, their bite in some instances being no worse than the sting of a hornet. The bite of the larger European Vipers may be very dangerous, and followed by fatal results, especially in children, at least in the hotter parts of the Continent; whilst the small _Vipera ursinii_, which hardly ever bites unless roughly handled, does not seem to be possessed of a very virulent poison, and, although very common in some parts of Austria-Hungary, is not known to have ever caused a serious accident. It is noteworthy that the size of the poison fangs is in no relation to the virulence of the venom. The comparatively innocent Indo-Malay _Lachesis_ alluded to above have enormous fangs, whilst the smallest fangs are found in the most justly dreaded of all snakes, the Hydrophids. Little is known of the physiology of the poison of the Opisthoglyphous Colubrids, except that in most cases it approximates to that of the Proteroglyphs. Experiments on _Coelopeltis_, _Psammophis_, _Trimerorhinus_, _Dipsadomorphus_, _Trimorphodon_, _Dryophis_, _Tarbophis_, _Hypsirhina_, and _Cerberus_, have shown these snakes to be possessed of a specific poison, small mammals, lizards, or fish, being rapidly paralyzed and succumbing in a very short time, whilst others (_Eteirodipsas_, _Ithycyphus_) do not seem to be appreciably venomous. Man, it is true, is not easily affected by the bite of these snakes, since, at least in most of those which have a long maxillary bone, the grooved fangs are placed too far back to inflict a wound under ordinary circumstances. There are, however, exceptions. A case was reported a few years ago of a man in South Africa nearly dying as a result of the bite of the Boomslang, _Dispholidus typus_, the symptoms, carefully recorded, being those characteristic of Viperine poisoning, an important fact to oppose to the conclusions, based on the physiological experiments on _Coelopeltis_, which appeared to disprove the theory that the Viperidæ may have been derived from Opisthoglyphous Colubrids.