48 Harvey and the [lect. 



The new theory of the circulation made for the first time 

 possible true conceptions of the nutrition of the body, it cleared 

 the way for the chemical appreciation of the uses of blood, it 

 afforded a basis which had not existed before for an under- 

 standing of how the life of any part, its continued existence 

 and its power to do what it has to do in the body, is carried 

 on by the help of the blood. And in this perhaps, more than 

 its being a true explanation of the special problem of the heart 

 and the blood vessels, lies its vast importance. 



We shall see presently how the new way thus opened up 

 by Harvey was followed with brilliant success, on the one hand 

 in England, and on the other hand in Italy. Meanwhile it 

 may be well to turn aside to tell in a brief way the story of 

 a special but yet important addition to our knowledge of the 

 blood system, which was being made at the very time that 

 Harvey was meditating over and developing his views. 



That the food which disappears from the alimentary canal, 

 during its passage along it, becomes in some way or other 

 blood, was a view which took origin in the early days of 

 mankind so soon as man began to consider what took place 

 within his frame. It was part of the Galenic doctrine that 

 the food thus utilized for the body, was taken up from the 

 alimentary canal by the vena porta, and carried to the liver 

 there to be enriched with the natural spirits and so concocted 

 into the blood which passed on to the heart. 



Galen himself quotes Erasistratus as having seen that, in 

 young kids which had lately sucked, the arteries in the 

 mesentery contained milk, and indeed had observed the same 

 thing himself. Eustachius too, the anatomist of Rome, who 

 flourished between Vesalius and Fabricius, whose name and 

 labours are preserved among us by the Eustachian tube and 

 Eustachian valve, saw apparently what we now call the thoracic 

 duct. Nevertheless it may be said that up to the early years 

 of the seventeenth century, anatomists were aware of one set 

 of vessels only, the blood vessels, arterial or venous. 



In the year 1622 Gaspar Aselli of Cremona, Professor of 

 Anatomy at Pavia, discovered the lacteals; and this is how 

 he relates his discovery : 



