Commentary for Shabbat 270:14
הא לא שהה ספיקא הוי
This is satisfactory on the view that a title to the usufruct is not as a title to the principal; but on the view that a title to the usufruct is as a title to the principal, what can be said?<span class="x" onmousemove="('comment',' V. B.B. 136a; the mother is the principal, while the child is the usufruct. On the latter view he is like a Jewish-born child ');"><sup>14</sup></span> — Said R. Mesharsheya: [It is possible] where one buys a female slave on condition that he will not subject her to a ritual bath.<span class="x" onmousemove="('comment',' There her child is certainly unlike a Jewish-born one. ');"><sup>15</sup></span> It was taught, R. Simeon b. Gamaliel said: Any human being who lives<span class="x" onmousemove="('comment',' Lit., 'tarries'. ');"><sup>16</sup></span> thirty days is not a nefel,<span class="x" onmousemove="('comment',' A nonviable, premature birth. ');"><sup>17</sup></span> because it is said, And those that are to be redeemed of them from a month old shalt thou redeem.<span class="x" onmousemove="('comment',' Num. XVIII, 16. Since he must then be redeemed, it follows that he is viable. ');"><sup>18</sup></span> An animal [which lives] eight days is not a nefel, for it is said, and from the eighth day and henceforth it shall be accepted for an oblation, etc.<span class="x" onmousemove="('comment',' Lev. XXII, 27. ');"><sup>19</sup></span> This implies that if it [an infant] does not last [so long], it is doubtful;