The advocates on the other side urge, that if after conception the orifice of the matrix were closed, there could be no superfoetation. To this it may be replied, that the seminal liquor may penetrate through the membranes of the matrix; that even the matrix itself may open to admit the superfoetation; and that at any rate superfoetations happen so rarely, that they make a very trifling exception to the general rule. Other authors have maintained, that this change never appears but in women who have conceived before, and borne children. In first conceptions, indeed, the difference must be less sensible; but be it as conspicuous as it may, ought we thence to conclude that it is a certain and positive sign? No; it is unaccompanied with sufficient evidence. Neither from the study of anatomy, nor from experiments, can we, as to this point, acquire more than general conclusions, which on a particular examination are often found to be highly erroneous. It is the same also with respect to the tremor or convulsive cold, which some women have said they felt at the time of conception. As most women do not experience this sensation; as others assure us, on the contrary, that they have felt a burning heat; and, as others still confess, that they are utter strangers to all such feelings; the natural conclusion is, that such signs are highly dubious, and that when they do happen, it is less perhaps in consequence of conception, than of other consequences. On this subject I shall add but one fact, from "Parson's Lectures on Muscular Motion," which proves that the orifice of the matrix does not close immediately after conception; or that at least the seminal fluid may even then find a passage into it. A woman of Charles-Town, in South-Carolina, was delivered, in 1714, of two children, one immediately after the other. To the utter astonishment of all present, one child was black and the other white. From this evident testimony of her infidelity to her husband, the woman acknowledged that a negro had one day entered her chamber, where her husband had just left her in bed, and by threats of immediate death compelled her to gratify his desires. This fact proves that the conception of two or more children does not always happen at one time, and gives great weight to my opinion, that the semen penetrates through the texture of the matrix.