DIFFICULTIES 



the terminal arteries and the veins, and he had to postulate 

 the existence of the capillaries, which were not discovered until 

 later. Harvey could not demonstrate the circulation, so had to 

 leave it as an inference. He required courage to announce how 

 much blood he calculated that the heart pumped out. Harvey 

 himself wrote : 



" But what remains to be said about the quantity and source 

 of the blood which thus passes, is of so novel and unheard-of 

 character that I not only fear injury to myself from the envy of 

 a few, but I tremble lest I have mankind at large for my enemies, 

 so much doth want and custom, that become as another nature, 

 and doctrine once sown and that hath struck deep root, and 

 respect for antiquity, influence all men : still the die is cast, and 

 my trust is in my love of truth, and the candour that inheres in 

 cultivated minds." ^"^ 



His fears were well founded for he was subjected to derision 

 and abuse and his practice suffered badly. Only after a struggle 

 of over twenty years did the circulation of the blood become 

 generally accepted. 



Other illustrations of resistance to new ideas are provided by 

 the stories about Jenner and Mules already recounted and that 

 about Semmelweis given later in this chapter. 



Vesalius in his early anatomical studies related that he could 

 hardly believe his own eyes when he found structures not in 

 accord with Galen's descriptions. Lesser men did, in fact, 

 disbelieve their own eyes, or at least thought that the subject 

 for dissection or their own handiwork was at fault. It is often 

 curiously difficult to recognise a new, unexpected fact, even 

 when obvious. Only people who have never found themselves 

 face to face with a new fact laugh at the inabihty of medieval 

 observers to beUeve their own eyes. Teachers well know that 

 students often ignore the results of their experiments and mistrust 

 their observations if they do not coincide with their expecta- 

 tions. 



In nearly all matters the human mind has a strong tendency 

 to judge in the light of its own experience, knowledge and 

 prejudices rather than on the evidence presented. Thus new 

 ideas are judged in the light of prevailing beHefs. If the ideas 

 are too revolutionary, that is to say, if they depart too far from 



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