MALPIGHI 



11 



But between this observation, which " invited 

 him to imagine " a theory, and his final proofs of 

 the circulation, lay a host of difficulties ; and it 

 is certain, from his own account of his work, that 

 experiments on animals were of the utmost help 

 to him in leading him " out of the labyrinth." 



III. — After Harvey, 

 i. The Capillaries. 



The capillary vessels were not known in 

 Harvey's time : the capillamenta of Caesalpinus 

 were not the capillaries, but the vevpa of Aristotle. 

 It was believed that the blood, between the smallest 

 arteries and the smallest veins, made its way 

 through " blind porosities " in the tissues, as water 

 percolates through earth or through a sponge. 

 The first account of the capillaries is in two letters 

 (De Pulmonibus, 1661) from Malpighi, professor 

 of medicine at Bologna, to Borelli, professor of 

 mathematics at Pisa. In his first letter, Malpighi 

 writes that he has tried in vain, by injecting the 

 dead body, to discover how the blood passes from 

 the arteries into the veins : — 



" This enigma hitherto distracts my mind, 

 though for its solution I have made many and 

 many attempts, all in vain, with air and various 

 coloured fluids. Having injected ink with a 

 syringe into the pulmonary artery, I have again 

 and again seen it escape (become extravasated 

 into the tissues) at several points. The same 

 thing happens with an injection of mercury. 



