552 GENERAL CONSIDERATIONS 



was an ebb and a flow of the blood. His classical work on the structure 

 of the human body was published in 1543. 



625. Harvey.— Harvey (1578-1657), an English physician (Fig. 333), 

 revived the experimental method in physiology. His most noteworthy 

 contribution was the proof of the circulation of the blood. Aristotle 

 believed that the blood was elaborated from the food in the liver, was 

 conducted to the heart and then out from the heart through the veins.- 

 He and others who followed him thought that the arteries contained no 

 blood but that they carried the vital spirits, or pneuma. Galen dis- 

 covered that the arteries did contain blood ; he distinguished nerves from 

 tendons, which look much like them, and believed the former carried the 

 pneuma. Vesalius proved that the two sides of the human heart were 

 completely separated, and Servetus (1511-1553) outlined the circulation 

 in the lungs. Jacobus Sylvius (1478-1555) described valves in the veins. 

 The complete circulation was first discovered and definitely described 

 by Harvey. He used no microscope, however, and neither saw the 

 capillaries nor demonstrated their existence; this work remained for 

 Malpighi and Leeuwenhoek. 



626. Microscopists. — The actual discovery of the microscope is 

 unknown, though by many its discovery is attributed to Galileo. With 

 the improvement of this instrument an era of discoveries began which 

 was to affect the whole future of biology. The earliest of the microsco- 

 pists and perhaps the most eminent was Malpighi (1628-1694), an Italian, 

 whose greatest work was done on the anatomy of the silkworm but who 

 among other observations saw the flow of the blood in the lungs and 

 mesenteries of the frog. Swammerdam (1637-1680) and Leeuwenhoek 

 (1632-1723) were Hollanders. The former, who was a physician and 

 naturalist, made extensive researches in the structure and life histories 

 of animals, mostly insects. He championed the preformation theory 

 (Sec. 630). The latter, who was a microscope maker, discovered red 

 blood corpuscles and observed the connections of capillaries with veins 

 and arteries in the tail of a tadpole; he first observed rotifers and a great 

 many minute organisms, including protozoans and bacteria. Hooke 

 (1635-1703), an English physicist and microscopist, discovered the cell. 

 The work of these men was followed by that of many others who unfolded 

 a wealth of detail in regard to minute anatomy and the smaller living 

 organisms. 



627. Comparative Anatomy. — To Cuvier (1769-1832) is ascribed the 

 founding of the science of comparative anatomy. He was the son of a 

 French army officer and early in his life showed a pronounced liking for 

 paleontology and zoology. Most of his life was spent in Paris, where he 

 occupied a commanding position in science. He was given a title, devoted 

 considerable time to public education, and was appointed chancellor of 

 the Imperial University by Napoleon. His great work was "Le Regne 



