16 And if any man's seed of copulation go out from him, then he shall wash all his flesh in water, and be unclean until the even.
17 And every garment, and every skin, whereon is the seed of copulation, shall be washed with water, and be unclean until the even.
What is the precise meaning of "whereon is" in verse 17? That is to say, while I'm sure we can all agree that a visible drop falling on a garment clearly qualifies, what if a clean garment accidentally rubs up against a dried drop that has fallen on a wood floor, a piece of leather, or a cloth item of some kind?
Considering that microscopic fragments of said dried drop could rub off and go into the clean garment that rubs against it, does the garment then qualify as one "whereon is the seed", and thus unclean?
Also, if the answer is that it does, is the same true if a drop on a wooden floor has been wiped or washed away, but microscopic fragments still remain (or if enough if left that an ultraviolet light would reveal the drop's former presence).