406 SOME GREAT NAMES IN BIOLOGY 



Life comes from Life. — Another group of men, after years of 

 patient experimentation, worked out the fact that life comes from 

 life. In ancient times it was thought that hfe arose sponta- 

 neously; for example, that fish or frogs grew out of the mud of the 

 river bottoms, and that insects came from dew or the rotting of 

 meat. But Redi (ra'de), who Hved 1621-1697, proved by a sim- 

 ple experiment that flies laid their eggs in rotting meat, and thus 

 accounted for the maggots found there. It was believed that 

 bacteria arose spontaneously in water, even as late as 1876, whei. 

 Professor Tyndall proved by experiment the contrary to be true. 



In 1651 William Harvey, the court physician of Charles I of Eng- 

 land, showed that Uving things came from egg cells. It was much 

 later, however, that the part played by sperm and egg cell in 

 fertilization was carefully worked out. It is to Harvey, too, that 

 we owe the discovery of the circulation of the blood. He showed 

 that blood moves in a complete circulation in the body and that 

 the heart pumps it. Up to his time the arteries had been thought 

 to be air tubes, because after death they were empty of blood. 

 He might be called the father of modern physiology as well as of 

 embryology. 



Van Leeuwenhoek (page 44), who lived 1632-1723, is remem- 

 bered as the maker of an improved microscope, although his 

 simple lenses were far from equaling our modern instruments. We 

 also connect his name with Harvey's work, for it was he who first 

 saw the circulation of blood in the capillaries. He says in speak- 

 ing of circulation in a tadpole's tail, that '' Thus it appears that 

 an artery and a vein are one and the same vessel, prolonged and 

 extended." 



A long list of other names might be added to show how gradually 

 our knowledge of the working of the human body has been in- 

 creased. At the present time we are far from knowing all the func- 

 tions of the various parts of the human engine, as is shown by the 

 number of investigators in physiology at the present time. Pres- 

 ent-day problems have much to do with the care of the human 

 mechanism and with its surroundings. The solution of these 

 problems will come from the application of hygiene, preventive 

 medicine, and sanitation. 



In the preceding chapters of this book we have learned some- 



