By: Ilay Ileri

Pulmonary Circulation
The teachings of the Galenical school about the pulmonary circulation are depicted here in Figure 2. A feature was that some of the blood in the right ventricle passed into the left ventricle through “invisible pores” in the interventricular septum. The existence of these so-called pores was a puzzle to some anatomists but they were a necessary feature of the Galen scheme because it was not appreciated that a large amount of blood flowed from the lungs to the heart.
In his Commentary on Anatomy in Avicenna’s Canon, Ibn al-Nafis made three important advances with respect to Galen’s scheme:

1. He stated categorically that the interventricular septum between the right and left ventricles was not porous, and could not allow blood to travel through it as was critical in the Galen model (Figure 2). Here is the English translation made by Meyerhof(15) of the section of the book by Ibn al-Nafis identified as fol. 46 r:
   
   “But there is no passage between these two cavities [right and left ventricles]; for the substance of the heart is solid in this region and has neither a visible passage, as was thought by some persons, nor an invisible one which could have permitted the transmission of blood, as was alleged by Galen. The pores of the heart there are closed and its substance is thick.”
   
   This forceful denial of the permeability of the interventricular septum is also repeated elsewhere in the commentary. For example, in the section identified as fol 65 r and v, Meyerhof’s translation is as follows:
   
   “There is no passage at all between these two ventricles; if there were the blood would penetrate to the place of the spirit [left ventricle] and spoil its substance. Anatomy refutes the contentions [of former authors]; on the contrary, the septum between the two ventricles is of thicker substance than other parts in order to prevent the passage of blood or spirits which might be harmful. Therefore the contention of some persons to say that this place is porous, is erroneous; it is based on the preconceived idea that the blood from the right ventricle had to pass through this porosity–and they are wrong!”
   
2. Since there is no communication between the right and left ventricles through the interventricular septum, it follows that the output of the right ventricle can only reach the left ventricle via the pulmonary circulation. In the section of the Commentary identified as fol. 46 r, Meyerhof’s translation reads: “the blood after it has been refined in this cavity [right ventricle], must be transmitted to the left cavity where the [vital] spirit is generated.” In the section identified as fol. 65 r and v, the translation reads, “For the penetration of the blood into the left ventricle is from the lung, after it has been heated within the right ventricle and risen from it, as we stated before.”
   
3. In a further short passage, Ibn al-Nafis states that there must be small communications between the pulmonary artery and the pulmonary vein. This was an inspired prediction of the existence of the pulmonary capillaries because these were not seen until 400 years later by Marcello Malpighi (1628-1694). Here is the translation of the relevant section in fol. 46 r, “And for the same reason there exists perceptible passages (or pores, manafidh) between the two [blood vessels, namely pulmonary artery and pulmonary vein]”. Figure 3 reproduces part of the Commentary relating to the pulmonary circulation in the original Arabic text. Figure 4 is a statement by Ibn al-Nafis in his own hand that one of his students has satisfactorily understood one of his other writings.
   
   It was not until 300 years later that scholars in Europe came to the same conclusion, that the blood had to pass through the pulmonary circulation and could not move directly from the right to the left ventricle. The first person to state this was Michael Servetus (1511-1553) who wrote
   
   “However, this communication is made not through the middle wall of the heart, as is commonly believed, but by a very ingenious arrangement the refined blood is urged forward from the right ventricle of the heart over a long course through the lungs; it is treated by the lungs, becomes reddish-yellow and is poured from the pulmonary artery into the pulmonary vein” (translation modified from O’Malley).(16) The Latin version is as follows. “Fit autem communicatio haec non per parietem cordis medium, ut vulgo creditur, sed magno artificio a dextro cordis ventriculo, longo per pulmones ductu, agitatur sanguis subtilis: a pulmonibus praeparatur, flavus efficitur: et a vena arteriosa, in arteriam venosam transfunditur”
   
   (text in Izquierdo(10) and Fulton(7) although the spelling is slightly different between the two).
   
   The statement was actually made in a theological treatise, “Christianismi Restitutio” (“The Restoration of Christianity”) which was considered heretical by both Catholics and Calvinists, and as a result Servetus was burned at the stake in Geneva. Only three copies of the book survive today. Later the same ideas were expressed by Realdus Columbus, his student Juan Valverde, Andreas Vesalius, and William Harvey.
   
   However, it is interesting that Harvey was initially puzzled by the physiology of the pulmonary circulation. For example, he stated, “It is altogether incongruous to suppose that the lungs need for their nourishment so large a supply of blood, so pulsatorily delivered”. (9) In fact, it was only a few years before his death that Harvey reported experiments where he conclusively demonstrated the passage of liquid from the pulmonary artery to the left ventricle. This was done in a letter to a German friend named Slegel. Harvey described how he had ligated various vessels in the lung of the cadaver of a man who had died as a result of strangulation, and showed how water passed freely through the lungs from the pulmonary artery to the left ventricle .(11)
   
   A fascinating sidelight on Ibn al-Nafis is how the manuscript Commentary on Anatomy in Avicenna’s Canon was made known to the Western world only about 80 years ago. A young Egyptian physician, Muhyo Al-Deen el Tatawi, came across the manuscript in the Prussian State Library in Berlin in the course of writing his doctoral thesis for the medical faculty of Albert Ludwig’s University of Freiburg im Breisgau, Germany.(20) The young doctor was subsequently employed by the Egyptian Public Health Service and transferred to small provincial towns where he could not carry out further research. Happily, Max Meyerhof, an eminent medical orientalist in Cairo, was made aware of the discovery and wrote a short commentary on Dr. Tatawi’s thesis to save it from oblivion. This was fortunate because the thesis was never published and only five type-written copies of it were made. Meyerhof subsequently published German, French, and English translations of the relevant parts of the Commentary of Ibn al-Nafis. One of these contains a reproduction of the Arabic text.(15)
   
   A final interesting question is whether Michael Servetus whose book was dated 1553, and later Colombus, Valverde, Vesalius, and Harvey were aware of the work of Ibn al-Nafis on the pulmonary circulation published over 300 years before. The statements on the pulmonary transit of blood by Ibn al-Nafis and Servetus are rather similar and might suggest that the latter was aware of the earlier work although one study points out that there are some inconsistencies between the two statements.(21) One reason for raising the issue is that in 1547 there was a Latin translation of another book by Ibn al-Nafis entitled Commentary on Compound Drugs. This dealt with the last part of Avicenna’s book The Canon of Medicine concerning lists of drugs. The translation was made by Andrea Alpago of Belluno but apparently it did not include any reference to the pulmonary transit of blood. Other translations of Alpago have also been discussed in this context.(12, 17) However, many historians believe that Servetus was not aware of the work of Ibn al-Nafis and if so, both deserve credit for the discovery of the pulmonary transit of blood.
   
   Note on Sources
   Many people have written short pieces about Ibn al-Nafis and so it might be useful to identify the primary sources that I have found helpful. First, there is the doctoral thesis by Tatawi, and the three articles by Meyerhof who was responsible for introducing the thesis to the scholarly community. Tatawi’s thesis and Meyerhof’s 1935b article in German both include reproductions of the Arab text. In addition, the articles by Chehade, and Haddad with Khairallah add interesting information and also reproduce the original text. In fact, the latter authors actually owned one of the original manuscripts. Bittar wrote a thesis on Ibn al-Nafis for Yale University and his three articles have much of interest. Sezgin(18) recently collected all these articles with others into a book which is invaluable.