Bacteria in Daily Life

by Grace C. Frankland

Six specimens of the mongoose were forwarded to Calmette from Martinique, and these particular animals, it was stated, had never been set at liberty since they were imported, so that they had had no previous experience of snakes or venom. On arriving at the laboratory, one of these little creatures was placed in a glass cage along with a large cobra. The cobra, at once rising up and dilating its neck, darted with fury upon the mongoose; but the latter, thanks to its extraordinary agility, escaped being caught, and took refuge, stupefied and terrified for the moment, in a corner of the cage. This stunned condition, however, did not last long, for just as the incensed cobra was preparing to make a fresh attack upon its insignificant little victim, the latter, with wide-open mouth, rushed and jumped upon the head of its enemy, viciously bit through its upper jaw, and broke its skull in a few seconds. Thus, although in size but a little larger than a squirrel, this tiny creature was more than a match for a cobra two yards long.

Artificial inoculations of cobra venom into the mongoose fully substantiated all the observed facts as to its remarkable immunity from this poison. A dose sufficient to kill a large rabbit in three hours was absolutely without effect; only when the venom was introduced in quantities amounting to as much as eight milligrammes was it followed by fatal results. Thanks, therefore, to their extraordinary agility and remarkable power of resisting the effects of this lethal toxin, these little animals are able to battle successfully with the most dangerous reptiles.

The rapidity with which serpent venom becomes absorbed by the system is almost incredible, and is well illustrated by the following experiment. A rat was inoculated with venom near the tip of its tail. One minute later the latter was cut off a short distance above the point of inoculation; but this operation was quite unable to save the animal's life, for even in that brief interval the poison had accomplished its fatal work, and a few hours later claimed its victim.

This rapid diffusion of the venom helps to explain the difficulty which is experienced in arresting the course of the poison by local treatment, for its passage is too rapid to permit of its being overtaken by superficial measures of even the most stringent character. But Calmette points out that local precautions are not to be neglected, for although they cannot nullify the action of the venom, they undoubtedly do delay its progress, and thus create a longer interval or respite, during which an opportunity is afforded for administering the anti-toxin. Before, however, passing on to the investigations which have culminated in the production of a specific antidote for this terrible toxin, there are a few more details which Calmette has furnished as to its character which are of interest. Serpent venom is characterised not only by its intensely virulent properties, but also by the tenacity with which it retains them under diverse circumstances. Thus it may be stored up for a whole year, and yet at the end of that time be as active as ever; and even after several years, although its toxic powers are somewhat reduced, it still retains them to a very appreciable extent.

Unlike the bacterial toxins, this venom toxin can stand exposure to considerable temperatures without injury to its activity, and that of the cobra only suffers after it has been submitted to 98° Centigrade for twenty minutes. Sensitiveness to temperature varies, however, with the snake from which the venom is derived. Thus the venom of the so-called "tiger-snake" of Australia will stand being exposed for ten minutes to from 100° to 102° degrees Centigrade, and its virulence only disappears when this temperature has been applied for twenty minutes. The venom of the "black snake," another Australian variety, loses its toxicity at a temperature of between 99° and 100° Centigrade; whilst an exposure to only 80° Centigrade for ten minutes is sufficient in the case of viper venom, according to Messrs. Phisalix and Bertrand, to profoundly modify its lethal action. A continuous exposure for a fortnight to a temperature of 38° Centigrade does not affect cobra venom in the least; but if during that same time it has been placed in the sunshine, it entirely loses all its lethal properties. Thus, a pigeon was inoculated with about thirty drops of venom which had been exposed to the sun's rays for fourteen days, and it survived; whilst another pigeon was inoculated with a little over six drops of similar venom which had been kept during this time in the dark, and it died in a quarter of an hour.

All these elaborate researches as to the character of serpent venom were essential to enable the next step to be taken in the elaboration of the antidote. Before this great achievement could be accomplished it was necessary to first succeed in artificially immunising animals against the effects of this powerful toxin, so that the serum of such animals could be applied for the protection and cure of other animals from the effects of snakebites.

It may be readily conceived that the task of artificially rendering animals immune from snake poison was not an easy one, for the process depends upon training the animal to gradually withstand larger and larger doses of the venom; and considering the intensely toxic character of the substance which had to be handled, the danger was ever present of the animal succumbing to venom poison before its serum had acquired the requisite pitch of protective power to render it of service as an anti-toxin. Dr. Calmette tells us that he carried out a very large number of experiments before he met with success. But it is not necessary here to discuss his various efforts; suffice it to say that at length his labours were rewarded, and the following extract from one of his memoirs describes the methods which he adopted for this purpose:—

"The best method of procedure for the purpose of vaccinating large animals destined to produce anti-venomous serum consists in injecting them from the outset with gradually increasing quantities of the venom of the cobra mixed with diminishing quantities of a one-in-sixty solution of hypochlorite of lime.[8] The condition and the variations in the weights of the animals are carefully followed, in order that the injections may be made less frequently if the animals do not thrive well. Quantities of stronger and stronger venom are in turn injected, first considerably diluted, and then more concentrated; and when the animals have already acquired a sufficiently perfect immunity, the venoms derived from as large a number of different species of snakes as possible are injected. The duration of the treatment is of considerable length—at least fifteen months—before the serum is sufficiently active to be used for the purposes of treatment."

An immense number of animals have been vaccinated by this method at the Pasteur Institute at Lille, where Dr. Calmette is now director; and in one of his memoirs we are told that they have horses there which have yielded during a period of eighteen months serum extremely active against venom. These horses receive in a single inoculation, without suffering the least inconvenience, doses of venom sufficient to kill fifty horses fresh to the treatment.

Large quantities of this serum have been forwarded from the Lille Institute to various parts of the world where venomous serpents are most frequently met with, and already important evidence has been collected as to its efficacy in cases of human beings bitten by dangerous reptiles. So impressed with its importance are Indian medical authorities, that its preparation has been included in the work which the new great bacteriological institute at Agra is carrying on.