CHAPTER V.
THE CHEMICAL STUDY OF SNAKE-VENOMS.
In the condition in which they are received on issuing from the glands, venoms always present the appearance of a thick saliva, of an oily consistency and more or less tinged with yellow, according to the species of snake by which the poison has been produced. They are entirely soluble in water, the addition of which renders them opalescent. Tested with litmus they exhibit a slightly acid reaction; this acidity, which is due to the presence of a very small quantity of an indeterminate volatile acid, disappears on desiccation, so that solutions of dried venom are neutral. The taste of venoms is very bitter. Their density, which is slightly greater than that of water, varies from 1030 to 1050.
Venoms are composed of a mixture, in variable proportions, of proteid substances, mucus and epithelial débris, fatty matters and salts (chlorides and phosphates of lime, ammonia and magnesia), with from 65 to 80 per cent. of water.
The elementary analysis of Cobra-venom made by H. Armstrong[7] gave the following results:—
| Carbon | 43·04 | per cent. |
| Hydrogen | 7·00 | “ |
| Nitrogen | 12·45 | “ |
| Sulphur | 2·50 | “ |
| Residue | Small quantities. | |
Not much is to be learnt from these figures; it would be of far greater importance to know the exact constitution of the proteid substances to which venom owes its physiological properties. Unfortunately, our knowledge of the chemistry of the albuminoid matters is still too imperfect for it to be possible for us to determine their nature.
As early as 1843 it was pointed out by Lucien Bonaparte that in the venom of Vipera berus the most important principle is a proteid substance to which he gave the name of viperin or echidnin, and which he compared to the digestive ferments. Later on Weir Mitchell and Reichert, and subsequently Norris Wolfenden, Pedlar, Wall, Kanthack, C. J. Martin, and MacGarvie Smith, showed that venoms, like diastases, exhibit a great complexity in composition; that all their characteristic toxic constituents are precipitable by absolute alcohol, and that the precipitate, when redissolved in water, recovers the properties possessed by the venom before precipitation.
According to Armand Gautier,[8] venoms contain alkaloids. The latter may be obtained, in very small amounts, however, by finely pulverizing dried venom with carbonate of soda, and systematically exhausting the mixture with alcoholic ether at a temperature of 50° C. These alkaloids have yielded crystallized chloraurates and chloroplatinates, and slightly deliquescent crystallized chlorhydrates. The latter produce Prussian blue when treated with very dilute ferric salts, and mixed with a little red prussiate. They therefore represent reductive bodies analogous to ptomaines.
Norris Wolfenden did not succeed in extracting these alkaloids from Cobra-venom, whence they had nevertheless been isolated by Armand Gautier. Wolcott Gibbs, and afterwards Weir Mitchell and Reichert, likewise failed to find them in Crotalus-venom. The toxicity of these bases is, moreover, but very slight, for the totality of the alkaloids extracted by A. Gautier from 0·3 gramme of Cobra-venom did not kill a small bird.