Each that we lose takes part of us — Menses

Each that we lose takes part of us; ¹
A crescent still abides,
Which like the moon, some turbid night,
Is summoned by the tides.

(F.1634/J.1605)

[1] part:: the blood that flows out of a woman's body.
[2] crescent:: the moon in her first quarter; the duration of menses.
[3] turbid:: disturbed, muddy, thick liquids of any kind.
[4] summoned, tides:: caused by the moon, a hint on menses.