vi CIRCULATION OF BLOOD: ITS DISCOVERY 171 



professorial chair, first at Pisa and then in Home, his ideas on the 

 circulation, without laying stress on their possible consequences 

 and eventual applications, no one would have contested with him 

 the glory of the discovery." Harvey, for the rest, was so far from 

 suspecting the wide-reaching consequences of the theory of the 

 circulation, as he had learned it from the Aretine, that it only 

 occurred to him to put it into print after publicly discoursing of 

 it to his pupils for nine years, when he was compelled to this 

 Course by the fact that the doctrine had brought him on the one 

 hand friends and disciples, on the other enemies and opponents, 

 and that these last were making a mighty disturbance. And even 

 after its publication in 1649, the physiological importance of the 

 theory appeared to him so problematical, that in his reply to 

 Eiolan, who refuted it, because he saw in it " neque efficientem, 

 neque finalem causam," he could find nothing better to say than 

 " Prius in confesso esse debet quod sit antequam propter quid 

 inquirendum. . . . Quod sunt in physiologia, pathologia et 

 therapeia recepta, quorum causas non novimus, esse tamen nullus 

 dubitat ? " 



Obviously, so long as the Aristotelian doctrine, as resuscitated 

 by Cesalpinus and Harvey, flourished, to the effect that the 

 function of the lungs consists in reviving the blood, and that these 

 organs, in which the blood becomes once more spirituous and 

 subtle, are nourished by the crude blood flowing back from all the 

 other organs ; so long, especially, as the laboratory for the blood, 

 and the paths by which the products of food digestion reached the 

 circulation, remained unrecognised for so long did the theory of 

 the circulation of the blood fall short of its true significance, and 

 appear to be merely a physiological curiosity. 



Certain passages of Galen indicate that Herophilus and 

 Erasistratus, the heads of the Alexandrian School (3000 B.C.), 

 observed the chyle vessels in the mesentery of sheep. At the 

 end of the seventeenth century Portal, and more than a century 

 previously Fracassato, pointed out that the celebrated Roman 

 anatomist Eustachius (Opuscula anatomica, Venetiis, 1564) in 

 studying the course of the azygos vein in the horse had recognised 

 the thoracic duct, and even detected some of its valves. It is 

 certain, however, that save for a vague tradition, all trace of these 

 fortuitous and isolated observations had been lost when the 

 Cremonese Gaspare Aselli, Professor of Anatomy at Pavia, found 

 the chyle vessels, which he termed lacteals, in the dog's mesentery, 

 in 1622. So fortunate did he esteem himself, as he relates, in 

 having found what he was seeking, that "conversus ad eos qui 

 aderant ; evprjKa inquam cum Archirnede." But he had no inkling 

 of the true function and physiological importance of these vessels. 



In the year 1648 Pecquet, a young physician of Dieppe, who 

 was studying at Montpellier, noted that the lacteals carried their 



