146 THE PATH OF SCIENCE 



have occurred in many branches of biology between 1838 

 and the present day. 



The rebirth of biolog)% then, started about 1537 in the 

 fields of human anatomy and physiology. Although A^esalius' 

 factual additions to knowledge ^vere considerable, his main 

 service to science ^vas to dare openly to doubt the authority 

 of the ancient writers. Greater discoveries than his were 

 made by others. Andrea Cesalpino, a man of extraordinarily 

 diverse interests in science, technology, and philosophy, de- 

 scribed the circulation of the blood in 1593 but, unfortu- 

 nately, failed to give particulars of the ^vay he got his kno^vl- 

 edge. It was left to the Englishman, William Harvey, to put 

 the physiology of the circulation on a really sound basis. His 

 Exercitatio anatomica de Motu Cordis et Sanguinis is de- 

 servedly one of the classics of science. He not only described 

 the path of the circulation but also made quantitative studies 

 of the amount of blood pumped by the heart. KnoTvledge 

 of human anatomy progressed rapidly, and by 1664 the 

 Oxford professor Thomas Willis had described the external 

 form of the brain and cranial nerves of man so accurately 

 that little of major importance has been added to his ac- 

 count. People had come at last also to understand that 

 glands are synthetic organs that pour out their secretions 

 through ducts. 



The object of Vesalius, Willis, and most of the other early 

 anatomists and physiologists was practical. They wished to 

 improve the art of medicine. Before biolog)' as a whole could 

 flourish, it was necessary that the true spirit of science shoidd 

 develop, that the study of nature should be undertaken as an 

 end in itself. A nuinber of people ^vere studying and classi- 

 fying plants during the sixteenth century, but they ^vere do- 

 ing so mainly because they ^vished to identify the species that 

 provided drugs and other substances of material value to man. 

 So long as this was so, real progress in botany could not be 

 made. The first person to treat the subject as an inde- 

 pendent science, without regard to practical applications, ^vas 



