We will not dwell longer here on the toxins of microbial origin. It appears evident, however, from what has been stated above, that the great majority, if not all, of the virulent microbes manifest their virulence by means of toxic secretions. Almost every one of these toxins has been the subject of study. They would otherwise not have interested us here, where our main object was but to dwell upon the general properties.
[CHAPTER V.]
THE VENOMS.
General Nature of Venoms.—The venoms are more or less toxic products secreted by certain reptiles, batrachians, and fish; by a large number of invertebrates; by arachnids, apids, scorpionids, araneids, and a large number of other insects.
The venoms are toxic principles very closely allied to the microbial toxins; like the latter, they form two classes, the one alkaloidal, the other proteid, possessing a true diastatic character. They closely resemble the microbial toxins, moreover, by the fact that they are capable of being transformed into vaccins by attenuation of their virulence, by the action of heat or chemical reagents, and of leading to habituation of use and the conference of immunity.[142] Moreover, like the various viruses, the serum of immunized animals is antivenomous, so that if injected into the veins or beneath the skin of non-immunized animals, the serum confers upon them an immunity against venom which lasts for some time.
These venoms, like the microbial toxins, possess but slight toxicity when absorbed via the stomach. Fraser, utilizing a method previously advocated, succeeded, by following this method, in vaccinating against serpent-venom by causing the absorption by animals of constantly increasing doses of venom.
It was thus possible to make the animals withstand doses a thousand times greater than the ordinary lethal dose; the blood and serums of these animals at this point possessed immunizing properties, and this property passed by heredity to the offspring, to which it is transmitted by the blood itself, and by the milk during feeding.
Along with these resemblances between the venoms and toxins, attention must be called to a very important difference. As we have already seen, the action of the toxins on the organism is always preceded by a certain period of incubation; the action of the venoms, on the contrary, is almost instantaneous, and in this respect they behave like chemical agents and alkaloidal toxins.
If the venoms are preserved in a moist condition, they change because they undergo putrefaction, which is generally the case with all diastatic substances, and particularly the toxins.
It is interesting to note that animals which have been bitten by a venomous serpent, but which, for some reason or other, have not succumbed to the venom, never recover their former condition; if they were young, their functions cease to develop, and they droop; if they are adults, their general condition remains that of stupefaction.