

IX 



THE DISCOVERY OF THE CAPILLARIES AND 



BLOOD CORPUSCLES 



HARVEY had demonstrated conclusively that the blood 

 did circulate. There was one part of the circulation, 

 however, that he left still a matter of inference. He had 

 shown that the blood passed from arteries to veins, but 

 he had not actually seen the passage. We now know that 

 the stream goes through the capillary network. To see 

 this, however, a microscope is necessary. 



The microscope had been discovered in Harvey's 

 time and long before the publication of his work on the 

 circulation of the blood. Galileo had demonstrated its 

 value as early as 1610. A few years later the instrument 

 was brought to England. Nothing of real importance, 

 however, was revealed by microscopic research until 

 after Harvey's death in his eightieth year in 1657. ^ 

 is therefore not remarkable that he made no use of the 

 instrument. A short time after his death his work 

 was completed by the investigations of certain micro- 

 scopic observers. 



The compound microscope, as we have seen, was first 

 made into an effective instrument by Galileo. It was, 

 as it were, a by-product of his invention of the telescope. 

 With his new instrument Galileo explored the heavens and 

 made many new and important discoveries. He demon- 

 strated the rings of the planet Saturn, he saw the satellites 



of Jupiter, and he examined the spots on the sun and the 



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