The reptile is placed in a large covered jar, containing a pad of absorbent wool impregnated with chloroform (figs. 86, 87), and in a few minutes it is stupefied. It is then grasped by the neck with the hands, and the edge of a plate is slipped between its jaws. On compressing the two poison-glands with the fingers, the venom dribbles out on to the plate.
A detailed description of this technique will be found in a note kindly drawn up for me by my friend Dr. Gouzien, late head of the Medical Staff of the French Settlements in India, and reproduced further on in the section of this book devoted to documents. The note in question was accompanied by figs. 17, 18, 19, 86, 87, and 88, which are reproduced from photographs, for which I am indebted to the kindness of M. Geracki, Engineer of the Savanna Spinning Mill at Pondicherry, Dr. Lhomme, and M. Serph, Assistant Surgeon-Dispenser.
The collection of the venom having been completed, the snake is put back into its cage again, the tail and the body being introduced first, and then the head. The lid or trap-door is half closed with the left hand, and, with a quick forward thrust, the right hand releases its grasp of the reptile and is immediately withdrawn; at the same time the left hand completes the closure of the cage. The snake is temporarily dazed, as though stunned, and it is only after the lapse of a moment that it thinks of darting open-mouthed at the walls of its prison.
When it is desired to procure large quantities of venom, as is indispensable in laboratories where antivenomous serum is prepared, the endeavour must be made to keep the snakes alive for the longest possible time. It then becomes necessary to resort to artificial feeding in the manner previously described (see p. 17), for they very often refuse to feed themselves.
Fig. 87.—Chloroforming a Cobra in order to Collect Venom, at the French Settlement of Pondicherry, in India (Stage II.).
Except when a snake is moulting, the venom can be extracted from its glands about every fortnight; and it is better that the extraction be not performed concurrently with artificial feeding, since, owing to the fact that the venom serves the animal as digestive juice, the reptile will soon perish if deprived of the means of digesting the food that it is obliged to receive. It is best, therefore, to select one day of the week for artificial feeding, and the corresponding day of the following week for the extraction of the venom.
When the venom has been collected, it must immediately be placed in a desiccator over calcium chloride or sulphuric acid, in order to dry it rapidly. In hot countries, and where no laboratory specially equipped for the purpose exists, it will suffice to dry the venom in a current of air, or even in the sun. It then concretes in scales of a citrin colour, more or less dark, according to the concentration of the liquid. In this dry condition, placed in well-corked bottles, protected from damp air, it may be kept almost indefinitely without losing anything of its original toxic power. On the contrary, if the desiccation be imperfect it undergoes a somewhat rapid change, and assumes a disagreeable odour of meat peptone. I have kept samples of various venoms, dried as described, for fifteen years without any sensible diminution of their activity.
Fig. 88.—Collecting Cobra Venom at Pondicherry (Stage III.).