THE CIRCULATION OF THE BLOOD 665 



produced in order to influence the activity of other organs. This function has 



FlG. 219. PORTEAIT OF HARVEY. 



(Photographed by Elliott & Fry from the picture by Mierevelt in the 

 Council Room of University College, London. The original 

 is in the possession of University of London, University 

 College. Reproduced by permission.) 



come especially into prominence in recent years in the theory of internal secretions, 

 or hormones. 



In the early stages this fluid is not confined to special channels, but passes 



