There have been several means proposed and practiced for checking conception. I shall briefly notice them, though a knowledge of the best is what most concerns us. That of withdrawal immediately before emission is certainly effectual, if practiced with sufficient care. But if (as I believe) Dr. Dewees' theory of conception be correct, and as Spallanzani's experiments show that only a trifle of semen, even largely diluted with water, may impregnate by being injected into the vagina, it is clear that nothing short of entire withdrawal is to be depended upon. But the old notion that the semen must enter the uterus to cause conception, has led many to believe that a partial withdrawal is sufficient, and it is on this account that this error has proved mischievous, as all important errors generally do. It is said by those who speak from experience that the practice of withdrawal has an effect upon the health similar to intemperance in eating. As the subsequent exhaustion is probably mainly owing to the shock the nervous system sustains in the act of coition, this opinion may be correct. It is further said that this practice serves to keep alive those fine feelings with which married people first come together. Still, I leave it for every one to decide for himself whether this check be so far from satisfactory as not to render some other very desirable. As to the baudruche, which consists in a covering used by the male, made of very delicate skin, it is by no means calculated to come into general use. It has been used to secure immunity from syphilitic affections. Another check which the old idea of conception has led some to recommend with considerable confidence, consists in introducing into the vagina, previous to connection, a very delicate piece of sponge, moistened with water, to be immediately afterward withdrawn by means of a very narrow ribbon attached to it, But, as our views would lead us to expect, this check has not proved a sure preventive. As there are many little ridges or folds in the vagina, we cannot suppose the withdrawal of the sponge would dislodge all the semen in every instance. If, however, it were well moistened with some liquid which acted chemically upon the semen, it would be pretty likely to destroy the fecundating property of what might remain. But if this check were ever so sure, it would, in my opinion, fall short of being equal, all things considered, to the one I am about to mention--one which not only dislodges the semen pretty effectually, but at the same time destroys the fecundating property of the whole of it. It consists in syringing the vagina immediately after connection with a solution of sulphate of zinc, of alum, pearl-ash, or any salt that acts chemically on the semen, and at the same time produces no unfavorable effect on the female.