Reference for Menachot 107:15

אמר רבה כל היכא דמעיקרא הוה ביה והשתא לית ביה הא לית ביה וכל היכא דמעיקרא לא הוה ביה והשתא הוה ביה מדרבנן

swelled so that it is now of the prescribed size until now it has been clean but from now onwards it is unclean!<span class="x" onmousemove="('comment',' I.e., it can become unclean since it is now the size of an egg; contra Resh Lakish and the others.');">¹⁸</span> - It is only so Rabbinically. If so, consider the next clause: And so it is, too, with regard to the flesh of an offering that w piggul or nothur.<span class="x" onmousemove="('comment',' This means, presumably, that if a piece of flesh that was piggul or nothar, and which was less than an olive's bulk (which is the minimum in regard to forbidden food) , had swelled to the size of an olive's bulk and one ate it, the penalty of kareth would thereby be incurred, for we estimate a thing according to its present size. For piggul and nothar v. Glos.');">¹⁹</span> Now if you hold that this rule<span class="x" onmousemove="('comment',' That we must consider everything according to its present size.');">²⁰</span> is Scriptural then it can well apply to piggul and to nothar; but if you hold that it is only Rabbinical, it will be asked: Is one liable [to kareth] for [eating] wha regarded as piggul or nothar Rabbinically?<span class="x" onmousemove="('comment',' Surely there is no penalty incurred, since by the law of the Torah there was not the prescribed bulk.');">²¹</span> - Render: And so it is, too, with regard to the uncleanness of what is piggul or nothar.<span class="x" onmousemove="('comment',' It is a Rabbinical ordinance that consecrated flesh that was rendered piggul or nothar is unclean and conveys uncleanness to the hands; v. Pes. 85a. We are now taught that if piggul or nothar less than an egg's bulk had swelled to the size of an egg, it will render the hands unclean.');">²²</span> For I might have said that since the uncleanness attaching to what is piggul or nothar is only a Rabbinic ordinance, the Rabbis would certainly not apply this rule<span class="x" onmousemove="('comment',' V. p. 324, n. 14.');">²³</span> to that which is only a Rabbinic ordinance; we are therefore taught [otherwise]. Come and hear: If the flesh of an old beast which was of the prescribed size had shrivelled up so that it is now less than the prescribed size, until now it could have been unclean but from now onwards it remains clean!<span class="x" onmousemove="('comment',' Thus contrary to Resh Lakish and the others who maintain that we must measure everything in the condition in which it was before.');">²⁴</span> - Rabbah explained the position thus: If a [forbidden] thing was of the prescribed size but now it is not so, then it is not so;<span class="x" onmousemove="('comment',' I.e., it is no longer a forbidden thing since it is not of the prescribed size. The term 'forbidden' is used here in an extended sense to include 'defilement'.');">²⁵</span> and if at first it was not of the prescribed size and now it is, then it is so Rabbinically.<span class="x" onmousemove="('comment',' By Rabbinical ordinance it is regarded as a forbidden thing.');">²⁶</span>

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