In the ordinary course of Nature women do not conceive before the menses appear, nor after they have ceased. The age at which men first acquire the powers of procreation is less distinctly marked. His body must obtain a certain degree of growth, before the seminal fluid can be produced; and before it can be formed and perfected, that growth must become still greater. This usually happens between the age of twelve and eighteen; but the period at which the procreative faculty of man ceases, Nature seems to have left undetermined. At sixty or seventy, when age begins to enfeeble the body, the seminal fluid is less copious, and often unprolific; yet there are many instances of men still continuing to procreate at the age of eighty or ninety. There also are examples of boys who have propagated at eight, nine, and ten years; and of girls who have conceived at seven, eight, and nine. But such facts are exceedingly rare, and ought to be classed as singular phenomena. The external sign of virility appears in infancy, but that is not sufficient; in order to accomplish the act of generation, there must be a previous production of semen; and this is never effected till the growth of the body is nearly finished. At first the quantity is very small, and for the most part unfruitful. Some authors have mentioned two signs of conception. The one is, a kind of tremor which they say begins at the time of conception, and continues for several days after; the other is taken from the orifice of the matrix, which they assure us is entirely closed after conception. These signs are, however, in my opinion, very equivocal, if not altogether imaginary. This tremor is mentioned by Hippocrates, and, according to him, it is so violent as to make the teeth chatter. Galen, on the authority of some women, imputes this symptom to a contraction of the matrix; others explain it by a vague sensation of cold over the whole body, and almost all establish the fact, like Galen, from the testimony of different women. Opinions, however, vary as to the changes which happen in the matrix after conception, some maintaining, that the edges of the orifice are drawn together so closely that there is not the smallest vacancy left between them; and others, that these edges are not exactly close till after the two first months of pregnancy. They nevertheless agree, that immediately after conception the orifice is closed by a glutinous humour; that the matrix, which, but for the pregnancy, might receive through its orifice a substance of the size of a pea, has no longer any perceptible aperture, and that the difference is so evident that a skilful midwife may distinguish it. If these assertions were true, even in the first days of pregnancy, its certainty or uncertainty might be ascertained.