Chullin 47

On today’s daf, the Gemara interrogates the color of a slaughtered cow’s lungs to determine whether or not its meat is kosher. 

Rava says: If the lung assumes a dark color like eye shadow, the animal is kosher. If its color is black like ink, the animal is a treifa. As Rabbi Hanina says: Blood that appears black is actually red, except that it decayed. If the lung was green, the animal is kosher, as can be derived from an incident with Rabbi Natan. And if it was red, it is kosher, as can also be derived from an incident with Rabbi Natan.

According to Rava, if one slaughters an animal and discovers that the lungs are completely black, it’s assumed they were seriously diseased and would have caused the animal’s imminent demise. Therefore, the animal is considered a treifa; it is not kosher. But if the lungs are a different color — particularly green or red — then the disease is not presumed to have been terminal. The animal is kosher.

How do we know green and red lungs are not markers of a terminal illness? Rabbi Hanina refers twice to an incident of Rabbi Natan. It turns out those were two incidents, as the Gemara now relates: 

As it is taught in a beraita: Rabbi Natan says: Once I went to the cities overseas, where one woman came before me who had circumcised her first son and he died. She had also circumcised her second son and he died. Out of concern that circumcising her third son might cause him to die as well, she brought him before me. I saw that he was red, so I said to her: “My daughter, wait for him until his blood is absorbed into him.” She waited for him until his blood was absorbed into him and then circumcised him — and he survived. They named him Natan the Babylonian after me. 

The Torah (Leviticus 12:3) commands that Jewish baby boys be circumcised on the eighth day of life. But this bereaved mother is understandably terrified to submit her third son to the required procedure. What, she asks Rabbi Natan, should she do? 

Rabbi Natan observes that the baby is unusually ruddy, and he determines that she should delay circumcision. The mother waits until the baby’s color seems more normal, and then allows him to be circumcised. The baby, thankfully, survives, and in gratitude she names him after Rabbi Natan. 

In a second nearly identical episode, Rabbi Natan once again travels abroad, this time to Cappadocia (modern-day Turkey). Once again, a twice-bereft mother brings her third baby to Rabbi Natan, terrified to proceed with circumcision. Rabbi Natan reports:

I saw that the baby was green. I looked at him and saw that he did not have the blood of circumcision in him. I said to her: “My daughter, wait until his blood enters him.” She waited for his blood to increase and then circumcised him — and he survived. They named him Natan the Babylonian after me. 

This time, the baby in question appears greenish in color. Rabbi Natan makes an opposite diagnosis. The red baby had too much blood; the green baby not enough. The mother waits until the baby’s skin appears normal, and just like in the first story, a successful circumcision follows and the grateful mother names the baby after Rabbi Natan.

The cases of Rabbi Natan are reported here to teach us that red and green skin indicate abnormalities that will resolve with time. That is why, according to halakhah, a slaughtered cow’s lung that appears green or red is determined to be exhibiting a temporary condition that would not have led to its demise. It is, therefore, not a treifa — it is kosher. 

The stories on today’s daf also speak to a real issue for Jewish baby boys in all generations. When the mitzvah of timely circumcision conflicts with the mitzvah of pikuach nefesh, protecting life, the latter wins out. Nowadays, parents may not consult rabbis, but they do check with medical professionals when a baby boy presents with various health complications in order to determine when it’s safe to proceed with brit milah. In such a case, delaying is not only permitted; it’s required. 

Read all of Chullin 47 on Sefaria.

This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on June 16, 2026. If you are interested in receiving the newsletter, sign up here.