4 o CIRCULATION OF THE BLOOD 



circulation, for instance, he made a most striking dis- 

 covery, but wholly failed to draw out its most important 

 lesson. 



In 1574 he published his book On the Valves of the 

 Veins. In it he says there are ' thin little membranes 

 on the inside of the veins distributed at intervals over 

 the limbs. At times they are single, at times we find two 

 of them together. Their mouths are directed towards 

 the root of the veins [that is, towards the heart], and in 

 the other direction [that is, away from the heart] they are 

 closed." (Plate VII. Fig. 5.) 



It is obvious to us now that these valves hinder the flow 

 of blood except in the direction of the heart. Indeed, 

 Fabricius shows this by an actual experiment that he 

 describes and figures. He shows that if an arm be 

 lightly bandaged so as to prevent the flow of blood back 

 to the heart, the veins of the arm will swell up. This 

 we now know is because blood can get into the veins of 

 the arm from the capillaries but cannot get out towards 

 the heart because of the bandage. In an arm so bandaged 

 the valves will show up as nodes or swellings in the course 

 of the veins. Fabricius actually draws attention to this 

 fact. Yet all he has to say in explanation is : 'In my 

 opinion these valves are formed that they may to a certain 

 extent delay the blood and so prevent the whole of it 

 flowing to the feet, the hands, or the fingers and collecting 

 there." He thus quite failed to recognise the true 

 function of these valves. He was still thinking on the 

 old Galenic lines of the ebb and flow of blood in the 

 veins. He was still thinking that the use of the veins 

 was to convey blood back and forth, carrying nutrient 

 matter and natural spirits from the heart to the tissues 

 and bringing back the impurities from the tissues. 



The great contribution of Fabricius to the problems 

 of the circulation was not so much his writing but his 



