הַפִּשְׂיוֹן מְטַמֵּא בְּכָל שֶׁהוּא וְהוּא שֶׁיִּהְיֶה הַפִּשְׂיוֹן מֵאַחַת מִמַּרְאוֹת הַנְּגָעִים. אֲבָל אִם הָיָה הַפִּשְׂיוֹן מַרְאֵה בֹּהַק אֵינוֹ פִּשְׂיוֹן. וְאֵין הַפִּשְׂיוֹן סִימַן טֻמְאָה עַד שֶׁיִּפְשֶׂה חוּץ לַנֶּגַע אֲבָל אִם פָּשָׂה לְתוֹךְ הַנֶּגַע הֲרֵי הוּא כְּמוֹת שֶׁהָיָה. כֵּיצַד. בַּהֶרֶת וּבְתוֹכָהּ בָּשָׂר חַי פָּחוֹת מִכַּעֲדָשָׁה וְהִסְגִּירָהּ וּבְסוֹף הַשָּׁבוּעַ נִתְמַעֲטָה הַמִּחְיָה מִמַּה שֶּׁהָיְתָה אוֹ שֶׁהָלַךְ הַבָּשָׂר הַחַי כֻּלּוֹ אֵין זֶה פִּשְׂיוֹן. שֶׁאֵין הַבַּהֶרֶת פּוֹשָׂה לְתוֹכָהּ אֶלָּא חוּצָה לָהּ:
The increase of a blemish imparts impurity regardless of its size, provided the increase was one of the shades of blemishes that impart impurity. If, however, the increase was the color of a bohak, it is not considered as an increase. An increase of a blemish is a sign of impurity only when it spreads beyond the blemish. If, however, it spreads within the blemish, the person's original status is unchanged. What is implied? There was a baheret with less than a lentil of healthy flesh inside of it. He was therefore isolated. At the end of a week, if the size of the healthy flesh was diminished or it disappeared entirely, it is not considered as an increase. For, to be significant, an increase of a baheret may not spread within its own midst, but rather outside of it.
