Nazir 53: How Much of a Skull, a Spine, a Corpse

We learn even more about when a nazirite has to shave because s/he has been in contact with tumah, a source of ritual impurity.  Today's daf focuses on how much of a substance is required to impart tumah.  A quarter-log?  A half-kav?  A barley-grain-bulk?  How do the requirements differ for blood, for bone, for segments of the spine or the skull?  Amud (b) discusses the case of a found, severed limb.  If that limb was attached to a person still living and if that limb could be theoretically reattached, it can impart impurity through carrying or contact but not while under a tent.

This incredibly lengthy examination of tumah with regard to nazirut is quite overwhelming.  Why did the rabbis choose to stay on this particular issue for so long?  There are so many issues that could benefit from the rabbis' attentions - why did they focus on how a nazirite would end his/her nazirut?

Perhaps this is simply an opportunity to discuss tumah.  The rabbi often focus on the lines that separate light from dark, this from that, ritual impurity from ritual purity.