THE RISE OF EXPERIMENTAL PHYSIOLOGY 21 



Next year Vesalius was driven by the hostility of the 

 medical profession to burn his manuscripts and relin- 

 quish original work; he was not yet thirty years of age, 



Galen had taught that there are two sets of vessels 

 in the body (arteries and veins), and that in each set 

 there is an ebb and flow. Knowing nothing of com- 

 munications between the ultimate branches of the 

 arteries and veins, and shrinking from the supposition 

 that the arteries and veins are entirely separate and 

 distinct, Galen had taught that the blood passes from 

 one set of vessels to the other in the heart. The 

 septum between the ventricles must be porous and allow 

 the blood to soak through. Vesalius did not venture 

 openly to challenge the physiology of Galen, but he 

 significantly admired the "handiwork of the Almighty," 

 which enables the blood to pass from the right to the 

 left ventricle through a dense septum in which the eye 

 can perceive no openings. Fabricius of Acquapendente 

 in 1574 demonstrated the valves of the veins, though 

 he never arrived at a true notion of their action. His 

 celebrated pupil, William Harvey, who had been anti- 

 cipated on important points by the Spaniard Michael 

 Servetus and Realdo Columbo of Cremona, published 

 in 1628 a clear account, supported by adequate experi- 

 mental evidence, of the double circulation through the 

 body and the lungs, and of the communications between 

 the arteries and the veins in the tissues — communica- 

 tions which it was reserved for the next generation to 

 demonstrate by the microscope. 



Aselli of Cremona rediscovered the lacteals in 1622; 

 they had been known ages before to Erasistratus, but 

 forgotten. Opening the abdomen of a dog, he saw a 

 multitude of fine white threads scattered over the 

 mesentery, and observed that when one of them was 



