I have 2 questions regarding the past few dapim:
1) Regarding the conclusion of the gemara that one can only fulfill his chiyuv of pru urvu if his children have children, how is it that one can have a chiyuv which can only be fulfilled by someone else, namely his children? Can I force my child to have children? Of course not, I can only try to teach them (which is of course another chiyuv of chinuch).
2) Is there an issur of non-surgical sterlization of females, such as drinking a potion as we have here in the gemara, or radiation therapy?
1) The Chiyuv of Pru u'Rvu is incumbent on an individual not on his children. However, Rav Yochanan rules that in the event that one's children die, he is required to "replace" them. One is only exempted from the obligation to bear children if his children survive. This renewed obligation is waived in the event that his children have children for it is considered that he has surviving progeny. This is not a transferal of the obligation to his children, rather an exemption on his own obligation.
2)The Shulchan Aruch (Even ha'Ezer 5,12) rules that a female may drink a potion with the intent to sterilize herself. However, there is a disagreement amongst the Poskim whether this applies to a married woman.(See Piskei Teshuva ibid. 11) As for radiation therapy a Rabbinical determination must be made if this constitutes a Ma'aseh which then would be prohibited even for a female. However, for medical reasons non- Ma'aseh sterilization may be permissible even for men. (See Shabbos 110b, Piskei Teshuva ibid. 10)