Halakhah for Niddah 86:69

תנוק בן יום אחד מטמא בזיבה ומטמא בנגעים ומטמא בטמא מת וזוקק ליבום ופוטר מן היבום ומאכיל בתרומה ופוסל (את) [מן] התרומה

it also follows that as a dead creeping thing conveys uncleanness through touch so does semen convey uncleanness through touch, but then, limiting it to its original basis, as semen conveys uncleanness to the man who emitted it, however small its quantity, so does it also convey uncleanness to the man who touched it, however small its quantity.<span class="x" onmousemove="('comment',' It has thus been shown that R. Hanilai's ruling is a point at issue between Tannas. Is it likely, however, that R. Hanilai would differ from the Tannas who presumably hold a different view? ');">⁵⁶</span> Said<span class="x" onmousemove="('comment',' In an attempt to remove the difficulty (cf. prev. n. second clause). ');">⁵⁷</span> R. Huna son of R. Nathan to R. Papa: Whence the proof that the inclusion in uncleanness of one who touched semen is deduced from the expression of 'Or whosoever occurring in the context dealing with the creeping thing?<span class="x" onmousemove="('comment',' Lev. XXII, 5, as presumed by R. Papa supra. ');">⁵⁸</span> Is it not possible that the inclusion is derived from the expression of 'Or from whomsoever the flow of seed goeth out,<span class="x" onmousemove="('comment',' Lev. XXII, 4. ');">⁵⁹</span> and<span class="x" onmousemove="('comment',' Since the deduction is not made from the contact of the creeping thing. ');">⁶⁰</span> all may be of the opinion that a deduction is to be carried through in all respects?<span class="x" onmousemove="('comment',' Sc. even if all were to uphold this view, uncleanness would nevertheless be conveyed by the touch of the smallest quantity of semen, since the inference is made, not from the uncleanness of the creeping thing but from that of the emission of semen which is conveyed by the smallest quantity. ');">⁶¹</span> The Tannas<span class="x" onmousemove="('comment',' Those who recited Mishnahs and Baraithas at the college; v. Glos. s.v. (b). ');">⁶²</span> were asked<span class="x" onmousemove="('comment',' To give a decision as to whether R. Papa or R. Huna was in the right. ');">⁶³</span> Some recited as R. Papa while others recited in agreement with R. Huna son of R. Nathan. <b><i>MISHNAH</i></b>. A GIRL ONE DAY OLD IS SUBJECT TO THE UNCLEANNESS OF MENSTRUATION. ONE WHO IS TEN DAYS OLD IS SUBJECT TO THE UNCLEANNESS OF <i>ZIBAH</i>. A BOY ONE DAY OLD IS SUBJECT TO THE UNCLEANNESS OF <i>ZIBAH</i>, AND TO THE UNCLEANNESS OF LEPROSY AND THAT OF CORPSEUNCLEANNESS; HE SUBJECTS [HIS DECEASED BROTHER'S WIDOW] TO THE DUTY OF LEVIRATE MARRIAGE;<span class="x" onmousemove="('comment',' Provided he was born prior to his brother's death. ');">⁶⁴</span> HE EXEMPTS [HIS MOTHER] FROM THE LEVIRATE MARRIAGE,<span class="x" onmousemove="('comment',' If he was born after his father's death though he only lived for a short while. ');">⁶⁵</span> HE ENABLES HER<span class="x" onmousemove="('comment',' His mother, the daughter of an Israelite, who was married to a priest, though the latter was dead when the child was born. ');">⁶⁶</span> TO EAT <i>TERUMAH</i> AND HE ALSO CAUSES HER TO BE DISQUALIFIED FROM EATING <i>TERUMAH</i>;<span class="x" onmousemove="('comment',' This is now presumed to refer to a priest's daughter who was married to an Israelite who died and was survived by a son one day old (v. Gemara infra.) ');">⁶⁷</span>

Sefer HaChinukh