It is a general supposition that such immunity, when congenital, is acquired _in utero_ by the inoculation of the parent, and Oliver Wendell Holmes' fascinating tale of "Elsie Venner" embodies many interesting features in this connection. Admitting such inoculation may secure immunity, recent experiments in the action of this as well as kindred poisons give no grounds for believing it at all universal or even common, but as depending upon occult physiological or accidental phenomena. For instance, the writer and his father are equally proof against the contagion and inoculation of vaccination and variola, in spite of repeated attempts to secure both, while their respective mothers suffered terribly with smallpox at periods subsequent to the birth of their children; and it is well understood that there are striking analogies between the poisons of certain contagious fevers and those of venomous serpents, inasmuch as one attack conveys exemption from future ones of like character. In other words, many animal poisons, as well as the pathological ones of smallpox, measles, scarlatina, whooping cough, etc., have the power of so modifying the animal economy, when it does not succumb to their primary influence, as to ever after render it all but proof against them. Witness, for instance, the ravages of the mosquito, that in certain districts punishes most terribly all new comers, and who after a brief residence suffer little, the bite no longer producing pain or swelling. Regarding the supposed correlation of serpent poison and the septic ferments of certain tropical and infectious fevers, they are not necessarily always contagious. It may be interesting to note that one Doctor Humboldt in 1852,[9] in an essay read before the Royal Academy of Medical Sciences at Havana, assumed their proximate identity, and advocated the inoculation of the poison of one as a prophylactic of the other. He claimed to have personally inoculated numberless persons in New Orleans, Vera Cruz, and Cuba with exceedingly dilute venom, thereby securing them perfect immunity from yellow fever. Aside from the extraordinary nature of the statement, the fact that the doctor affirmed, he had never used the virus to an extent sufficient to produce any of its toxic symptoms, cast discredit over the whole, and proofs were demanded and promised. This was the last of the subject, however, which soon passed into oblivion, though whether from failure on the part of the medico to substantiate his assertions, or from the inanition of his colleagues, it is difficult to determine, though the presumption is largely in favor of the former. Nevertheless, it is worthy of consideration and exhaustive experimentation, since it is no less plausible than the theory which rendered the name of Jenner famous. [Footnote 9: London _Lancet_.]