Bloodletting involves spilling small quantities of blood. It was used both as a cure and as a general preventive therapy that was believed to keep a person healthy. Bloodletting was based on an ancient system of medicine in which blood and other bodily fluid were considered to be humors, the proper balance of which was believed to maintain health. It was the most common medical practice performed by doctors on both humans and animals from antiquity through the late 19th century, a period of almost two millennia. Today it is well established that bloodletting is not effective for most diseases. The only remaining condition for which it is used is Polycythemia vera, a disease in which the body produces too many red blood cells.
Even in Talmudic times the Sages recognized the potential danger involved in bloodletting, and there were several methods undertaken to reinforce the body afterward. Eating meat in general, and eating organs from the circulatory system in particular, e.g., the spleen, is useful in restoring lost blood and replenishing hemoglobin after bloodletting. Wine accelerates circulation, as does warming oneself by a fire. Based on this the Gemara relates the following about bloodletting and drinking wine.
Shmuel, on the day on which he would perform the practice of bloodletting, they would prepare for him a dish of cooked spleen. Rabbi Yohanan would drink wine after bloodletting until the odor emerged from his ears. And Rav Nahman would drink until his spleen floated in wine. Rav Yosef would drink until the wine would emerge from the bloodletting incision. Rava would search for wine that was sufficiently aged such that three leaves had already grown over three years on the vine from which the grapes were picked.
Rav Nahman bar Yitzhak said to the Sages: I beg of you, on the day that you undergo bloodletting, tell your households, your wives: Nahman bar Yitzhak happened to come to visit us. Due to the visit of the important guest, the women will prepare a large meal. The husbands will eat well, recover from the lost blood, and avoid endangering themselves.