DAF DISCUSSIONS - CHULIN 72

Sam Kosofsky asked:

Rebbe,

Our maggid shiur noted that the average adult has about 5 liters of blood. Today's daf (72 amud alef) says that a reviis is the minimum amount needed to sustain life. Hayitachain?! A revvis is the size of a kiddush cup, 3.4 ounces or a little more. Even a Chazon Ish shiur is only 5.3 ounces. What did the gemara mean? If a person loses 40% of his blood or a little more he will not live long. I asked a frum doctor who has semicha and he also didn't know what the gemara meant. Can you shed some light.

B'kavod,

Sam Kosofsky, Hillcrest, Queens NY

The Kollel replies:

(a) The simplest answer would be that the Gemara is referring to a small, newborn baby. It means to say that no baby can survive with less than a Revi'is of blood. This would parallel the method Chazal used to determine that the Shiur of a Sheretz that is Metamei. A k'Adashah of Sheretz is Metamei since the smallest Sheretz (a snail) starts out its life at that size (see Chagigah 11a, and Rashi to Chulin 122a DH Chomet).

Unfortunately, this explanation does not seem to hold water. It is clear from a number of sources in the Gemara that even an adult survives on but a Revi'is of blood. This is evident from Sotah 5a (which implies that a grown man only has a Revi'is of lifeblood), and especially from Shabbos 129a (which says that a blood-letter sometimes leaves a person with exactly one Revi'is of remaining lifeblood, and not a drop more).

(b) Tosfos in Sotah 5a (and the Aruch) cites Rabeinu Chananel who apparently is addressing your question. Rabeinu Chananel explains that the Gemara is referring to a Revi'is of particularly "clear blood, which is the basis of the heart['s function]." If so, this "clear blood" (which we may call "lifeblood"), perhaps just enough to fill the heart's cavity, circulates along with the rest of the blood. Should one's lifeblood be reduced to less than a Revi'is, he cannot survive. The source for this diagnosis must be a Halachah l'Moshe mi'Sinai (as Rashi indeed states, Sotah ibid., see Maharatz Chiyus there).

(c) According to Rabeinu Chananel, the amount of lifeblood in a person seems to be constant, no matter how big or small the person is (as can be inferred from the wording of the Gemara in Sotah). This does not seem to be the opinion of Rashi in Shabbos 129a, who implies that the amount varies but can never be less than a Revi'is. Nevertheless, Rashi may also be referring to a particular current of "lifeblood" which circulates along with the rest of the blood, as Rabeinu Chananel explained.

(d) I would suggest an alternate explanation as follows. When enough blood leaves the body, blood pressure drops to the extent that it no longer can flow through the blood vessels. Perhaps the Gemara means that a person can survive as long as he has one Revi'is *more than* the amount of blood necessary to keep the heart pumping.

Best wishes,

Mordecai Kornfeld