vn] of the Seventeenth Century. 183 



were to be reached mainly by way of experiment, and as a 

 physiologist he like Harvey sought for truth in experiments 

 on living animals. And his experiments led him to truth. 

 His exposition of the circulation though less formal than that 

 of his contemporary Borelli, for Borelli was teaching while Lower 

 was experimenting and practising, not bristling as does Borelli's 

 with mathematical formulae and scholastic theorems and lem- 

 mas, comes in many respects much nearer the truth, is much 

 more like a modern exposition, and may with profit be read at 

 the present day. 



But it is not to Lower's views on the heart and circulation 

 that I wish now to call attention. In his work on the heart 

 there is included the account of experiments having results 

 fundamental in the history of respiration. 



It was known of course of old that venous blood was dark 

 and arterial bright, but the change was thought to take place 

 in the heart, on the left side of the heart ; and this view was 

 maintained even after the circulation through the lungs had 

 been accepted (though van Helmont seems to have caught 

 sight of the truth that the change might take place in the 

 lungs). Moreover the change in colour was thought to be only 

 a superficial accompaniment of profound differences between 

 the blood in the arteries and the blood in the veins. 



Lower's careful quantitative determinations and calculations 

 of the flow of blood through the heart raised as he says doubts 

 in his mind as to " whether there could be that great difference 

 " between venous and arterial blood which the vulgar think." 



He suspected that the change of colour took place in the 

 lungs as the contents of the pulmonary artery found their way 

 into the pulmonary veins, and that it was due simply to the 

 exposure of the blood to the air in the lungs. But so long as 

 he made observations on natural breathing he failed to satisfy 

 himself of the correctness of his supposition. 



Hooke's experiment on artificial respiration gave him the 

 opportunity he desired. Examining the lungs of an animal kept 

 alive by artificial respiration after the chest had been opened, 

 he had no difficulty in ascertaining that the blood in the pul- 

 monary veins long before it reached the heart was florid in 



