The first case is the secretion caused by some disease affecting a man"s sexual organs. The Hebrew word basar, translated "flesh" ( Leviticus 15:2, et al.) has a wide range of meanings. In this context it clearly refers to the woman"s vagina ( Leviticus 15:19) and so apparently to the man"s penis in Leviticus 15:2-3. The writer did not describe the physical problem in detail. The terms used seem to refer to either a diseased flow of semen (gonorrhea) or a discharge of pus from the urethra. [1] In either case this was a fairly lengthy ailment ( Leviticus 15:3). [source][source][source]
Another possibility is that this first case describes some affliction that both men and women suffered, such as diarrhea. The Hebrew words translated "any man" ( Leviticus 15:2) permit this. However the structure of the chapter and the references to the sexual organs argue against this view. [source][source][source]
Note that things that the man sat on during his defilement, those things under him (bed, chair, saddle), became unclean and a source of defilement themselves. Also any direct contact with an unclean man resulted in uncleanness for those who touched him ( Leviticus 15:7). Here basar evidently refers to any part of the man. [source][source][source]
"It is the uncleanness of the man and its consequences that are the main concern of this section. The striking thing about the uncleanness associated with these discharges is that not only the affected person becomes unclean, but also people and objects that come in contact with him, and these in their turn can become secondary sources of uncleanness. In this regard the uncleanness described here is much more "infectious" than the uncleanness of skin diseases dealt with in chs13-14.... In this respect, then, gonorrhea in men and menstrual and other female discharges are viewed as much more potent sources of defilement than others." [2][source]
Nevertheless the uncleanness that these discharges caused was less serious ritually than those associated with skin disease. The man could live at home; he did not need to move outside the camp. He just had to wash and wait until evening ( Leviticus 15:16; Leviticus 15:18); he did not need to go through a more elaborate ritual. He also needed to offer only two inexpensive sacrifices ( Leviticus 15:14; cf. Leviticus 14:10-20). [source][source][source]