Reference for Niddah 37:50

אלא הכא אי דם טהור ליכא במאי פליגי

But have we not learnt, FIVE KINDS? — R. Hanina replied: Black blood is really red [blood] that had deteriorated.<span class="x" onmousemove="('comment',' The two colours may, therefore, be treated as one. ');">⁴⁵</span>

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