Midrash su Levitico 15:24

1) (Vayikra 15:24) ("And if a man lie, lie, with her, then her niddah state shall be upon him, and he shall be unclean for seven days; and every mishkav on which he lies shall be unclean.") "lie, lie": to include two manners of lying (i.e., natural coitus and unnatural [sodomy]). "And if lie, lie": to include peripheral (non consummated) contact. "a man": to exclude a minor. I might think to exclude one of nine years and a day (or older). It is, therefore, written "and if he lie, lie." (and one of that age comes within the context of "lying.")

2) "with her" (a niddah): to exclude a woman leper (i.e., If one has coitus with her, her state of "leper" is not upon him.) (For without a verse) would it not follow a fortiori (that her state is upon him, viz.:) If a niddah, who does not confer tumah (upon all that is in a house), by entering it, does confer tumah upon one who cohabits with her, then a leprous woman, who does confer tumah by entry, how much more so should she confer tumah upon one who cohabits with her! It is, therefore, written "with her" (a niddah), to exclude a woman leper.

3) "then her niddah state shall be upon him." I might think that he followed her schedule (e.g., if he cohabited with her on her third day, he completes another four days as she does, and immerses and becomes tahor); it is, therefore, written "and he shall be unclean for seven days" (even if he cohabited with her on her seventh day). Let it be written "and he shall be tamei seven days." Why "then her niddah state shall be upon him?" I might think that he does not confer tumah upon men and earthen vessels; it is, therefore, written "then her niddah state shall be upon him" — Just as she confers tumah upon men and earthen vessels, so does he. I might then think that just as she confers tumah upon a mishkav to confer tumah upon men and garments, so does he. It is, therefore, written "then her niddah state shall be upon him, and every mishkav on which he lies shall be unclean." Let this ("and every mishkav, etc.") not be written, (for we can learn this from "then her niddah state, etc.") Its purpose must be, then, to cut him off from stringent tumah (that his mishkav not be as stringent as hers, to confer tumah upon men and vessels upon it) and to bring him to lesser tumah, that (his mishkav) confer tumah only upon food and drink.