THE discovery of the pulmonary circulation is an interesting and debated subject. At least five' discoveries are reported and statues have been erected in honor of the authors.Erasistratus of the Alexandrian School believed that the arteries and the left side of the heart were empty and served to convey the spirit of life to the body. This teaching persisted until Galen disposed of it in the second century A.D., for he showed that by pricking any artery of a living mammal blood gushed forth. He taught that most of the blood from the right side of the heart went through invisible pores in the septum to the left side of the heart. There it mixed with air to create spirit and was distributed to the body. A small portion of this blood in the left side passed back to the lung with each systole to be cleansed of its "soot." He indicated, however, that a small portion of the blood from the right side passed through the vena arteriosa and then by way of the arteria venosa reached the left side. We see, therefore, that Galen had a vague idea of the pulmonary circulation. His errors were a belief in the permeability of the septum and in the systolic reflux.In I553 A.D., Michael Servetus2 described the pulmonary circulation and denied the permeability of the septum but upheld the Galenic theory that the blood in the arteria venosa was mixed with the inspired air and cleansed of its "soot" by expiration.Fourteen centuries-from Galen to Servetus-pass in silence. During most of this period Arab civilization, besides preserving Greek medicine, made valuable contributions. A manuscript in our possession shows that in the thirteenth century a clear conception of the pulmonary circulation was contributed by Ibn Nafls,3 dean of the Mansoury Hospital in Cairo, Egypt. * A few days ago our attention was called to a valuable article by Dr. Max Meyerhof of Cairo entitled "Ibn An-Nafis (XIIIth Cent.) and His Theory of the Lesser Circulation," published in the June issue of Isis (No. 65, vol. XXIII. I, pp. IOO-I20). We had corresponded with Dr. At-Tatawi Bey and in his answer he stated that he had turned over his data to Doctor Meyerhof and' had referred our letter to the latter. In his second letter dated March 26, I935, At-Tatawi Bey, stated that he had received an answer from Doctor Meyerhof in which he gives reference to two manuscripts but no mention of any publication or article on the subject. 8Abui-l-lIasan Ala-ud-Din Ali ibn Abi-1-Hazm (known as Ibn Nafis). Brockelmann calls him Abu-el-Harm. The z and r, in Arabic, look-very much alike with the exception that the z has a dot over it. Evidently Brockelmann overlooked the dot over his r, 1

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