In order to ensure that it will keep for a long time, care is then taken to heat the hermetically sealed bottles in a water-bath at a temperature of 58° C. for one hour, and this operation is repeated for three days in succession. Serum prepared in this way preserves its antitoxic power unimpaired for about two years, _in all climates_. I have had occasion at various times to receive bottles which had been sent eighteen months and two years previously to India and Indo-China, and I was able to show that their standard had not perceptibly deteriorated. It was only the appearance of the contained liquid that was slightly changed; it was discoloured, and when shaken small white flakes were seen floating through it. These flakes are not a sign of deterioration; they are composed of deposits of precipitated albumin. They can be partly dissolved again by violent shaking, or they may be separated before use by filtration through sterilised paper. In a dry state, antivenomous serum may be kept for an almost indefinite period, in hermetically sealed glass tubes. In this condition it is usually divided into doses of 1 gramme, and when it is desired to make use of it, it is sufficient to dissolve a dose in 10 c.c. of water which has been boiled and allowed to cool, which takes two or three minutes. This solution is then injected beneath the skin, as though it were liquid serum. The Pasteur Institute at Lille prepares in this way large quantities of antivenomous serum, which are sent all over the world to those countries in which poisonous snakes are most dangerous. Recently, special laboratories for the production of this preparation have been instituted at Bombay and at Kasauli, in the Punjab, by Drs. G. Lamb and Semple; at Philadelphia, by Professor McFarland; at São-Paulo, in Brazil, by Dr. Vital Brazil; and at Sydney, by Dr. Tidswell. * * * * * _Specificity and Polyvalence of Antivenomous Serums._--By means of a large number of experiments I have proved that snake-venoms, whatever their origin, contain two principal substances: _neurotoxin_, which exerts its effects upon the elements of the nervous system, and _hæmorrhagin_ (Flexner and Noguchi), or _proteolytic diastase_, the effects of which remain exclusively local when the venom is introduced subcutaneously into the cellular tissue, but which produces coagulation of the blood when the venom is injected directly into the blood stream. The venom of COLUBRIDÆ in general is characterised by the constant predominence of _neurotoxin_, to which it owes its extreme toxicity, which is especially intense in the case of cobra-venom. It contains no, or scarcely any _hæmorrhagin_; for this reason the local symptoms of poisoning by COLUBRINE venom are almost _nil_. This _neurotoxin_, as we have seen, shows itself very highly resistant to heat.