106 THE ENGINES OF THE HUMAN BODY 



are so narrow that the red blood discs have to pass 

 along them in single file. Time has shown that these 

 fine channels or capillaries are the vessels which irrigate 

 and nourish the tissue-fields of the body ; the arteries 

 are the pipes or viaducts conducting the blood to these 

 fields ; the veins are merely the canals which Nature, 

 ever economical in her contrivances, uses for bringing 

 the blood back to the central pump — the heart. The 

 capillary network is the essential part of the vascular 

 outfit of the body. Harvey never saw the capillary 

 field, but it was his discoveries which gave us the key 

 that unlocked its secrets. Harvey made the merest 

 tyro in medicine wiser than the most renowned of ancient 

 physicians. 



When we look beneath the surface of things we see 

 a similarity in the triumphs of Columbus and of Harvey. 

 Columbus, from a survey of facts, became convinced that 

 the earth was a sphere ; no other theory could explain 

 the facts. If the earth was a sphere, then it was possible 

 to reach the Indies by sailing westwards as easily as by 

 sailing eastwards, the route discovered by the Portuguese. 

 On the strength of that belief Columbus followed the 

 setting sun across the Atlantic, and had the courage to 

 keep on when all his companions wanted to turn back, 

 and thereby discovered for Europe a new continent. 

 From an examination of valves and a study of the flow 

 of blood in the vessels Harvey became convinced that 

 there must exist communications between arteries and 

 veins, and thereby he gave the world of learning a new 

 continent of knowledge. 



I have compared Harvey to Columbus, but there is 

 another man — named by his creator Sherlock Holmes — 

 with whom he may also be compared profitably. For a 

 real man of science like Harvey is a detective- — a 

 detective of Nature's secrets. There was a day, the 

 reader will remember, when Sherlock Holmes, sitting in 

 his rooms in Harley Street, surprised a friend by accusing 

 him of having been at a certain post-office and having 

 sent off" a telegram to a certain person. The explanation 



