If medical science were a positive science, as is mathematics, and its professors able to apply its principles to daily life with the certainty of geometrical propositions, it would be folly to do otherwise than accept any medical opinion of established authority with entire confidence. This, however, is not the case, and the members of the medical profession would themselves be the last persons to lay claim to the possession of absolute truth. As centuries roll on, one medical school of opinion succeeds another, and theory after theory is exploded by accumulating facts. It is therefore no new thing and no subject of reproach to the self-sacrificing members of a noble profession, that different opinions should exist amongst them, in relation to subjects which affect that complex problem--human life. Indeed, it would be an exception to a general rule did not such difference exist. But we are now considering a subject so fundamental in human welfare, so much wider than any class interest, that any variety of opinion respecting it, is of vital importance to be noted, and must be recognised by all intelligent persons. It must therefore be thoroughly understood by all parents that there are now two distinct classes of medical opinion existing amongst physicians. Each class embraces men of high medical repute, but men who hold diametrically opposite views in relation to the guidance of the sexual powers, the one class considering Virtue, the other Vice, a necessity. Each class of physicians is honest in opinion, clear-sighted, wishing well to society; but the one class is far-sighted, the other near-sighted; the one knows the omnipotence of Good, the other sees the triumph of Evil. This diversity of opinion cannot remain as an abstract proposition, but, like all opinion, it expresses itself in action. In medical advice given to a youth, the slightest bias in one or another direction at the starting-point of life will set him on one of two paths constantly diverging to the right or wrong. One path leads to self-control, enlarged mental and physical hygiene, chastity; the other to doubt, yielding, fornication.