שִׁכְבַת זֶרַע מֵאֲבוֹת הַטֻּמְאָה מְטַמְּאָה אָדָם וְכֵלִים בְּמַגָּע וּכְלֵי חֶרֶס בָּאֲוִיר וְאֵינָהּ מְטַמְּאָה בְּמַשָּׂא וְאֵין הַמִּתְטַמֵּא בָּהּ מְטַמֵּא בְּגָדִים בִּשְׁעַת מַגָּעוֹ. וְאֶחָד הַנּוֹגֵעַ בָּהּ וְאֶחָד הָרוֹאֶה אוֹתָהּ בִּבְשָׂרוֹ שְׁנֵיהֶן רִאשׁוֹן לְטֻמְאָה דִּין תּוֹרָה. וְכַמָּה שִׁעוּרָהּ לְנוֹגֵעַ בְּכַעֲדָשָׁה וְלָרוֹאֶה בְּכָל שֶׁהוּא. וְאֵין הָרוֹאֶה טָמֵא עַד שֶׁתֵּצֵא מִמֶּנּוּ וְיַחְתֹּם מִמֶּנּוּ פִּי אַמָּה שֶׁנֶּאֱמַר (ויקרא טו לב) (ויקרא כב ד) "אֲשֶׁר תֵּצֵא מִמֶּנּוּ שִׁכְבַת זָרַע". לְפִיכָךְ אֲפִלּוּ רָאָה בְּקֵיסָם הוֹאִיל וְהִגִּיעָה לְפִי אַמָּה נִטְמָא. וְאֶחָד הָרוֹאֶה מֵחֲמַת בְּשָׂרוֹ אוֹ הָרוֹאֶה בְּאֹנֶס טָמֵא:
Semen is a primary source of impurity and imparts impurity to persons and implements when touched and to an earthenware container, when it enters its inner space. It does not impart impurity when carried and one who touches it does not impart impurity to his clothes even when touching it. It imparts impurity both to one who touches it and one who discharges it. They are both primary derivatives of impurity according to Scriptural Law. What is the measure that imparts impurity? For one who touches it, an amount the size of a lentil. For one who discharges it, the slightest amount. A man who discharges it is not impure until it leaves his body, reaching the orifice of the male organ, as implied by Leviticus 22:4: "From whom is discharged semen." Therefore even one who discharges semen through a reed, is impure because the semen reached the orifice of the male organ. One is impure whether he discharges semen as a natural physical reaction or due to forces beyond his control.
