Reference for Chullin 145:34

וכי מי טיהרו לאבר זה מידי נבלה

They replied: It is often the ca that an act' has a greater effect upon that which is not part of itself than upon that which is part of itself; we have learnt: Whatsoever is cut off from the foetus within the womb [and left inside] may be eaten, but whatsoever is cut off from the spleen or the kidneys [of the animal and left inside] may not be eaten.

Jastrow