452 ANIMAL BIOLOGY 



investigation in general broke away from the yoke of authority, 

 and men began to trust and use their own powers of observation. 

 (Fig. 290.) 



The work of Vesalius was on anatomy, and physiology was 

 treated somewhat incidentally. The complementary work on the 

 functional side came in 1628 with the publication of the epoch- 

 making monograph On the Motion of the Heart and Blood in Ani- 

 mals by Harvey (1578-1657) of London. No rational conception 

 of the economy of the animal organism was possible under the 

 influence of Galenic physiology, and it remained for Harvey to 

 demonstrate by a series of experiments, logically planned and 

 ingeniously executed, that the blood flows in a circle from heart 

 back to heart again, and thus to supply the background for a 

 proper understanding of the physiology of the organism as a whole. 

 With the work of Vesalius and Harvey, biologists had again laid 

 hold of the great scientific tools — observation, experiment, and 

 induction — which since then have not slipped from their grasp. 

 (Figs. 121, 291.) 



C. The Microscopists 



During this revival period, when collections and accurate de- 

 scriptions of plants and animals were being made and the study of 

 anatomy and physiology was going rapidly forward, optical inven- 

 tions occurred which were destined to make possible modern 

 biology. First came the development of the simple microscope, 

 through an adaptation of the principles of spectacles, during the 

 sixteenth century; then the combination of lenses to form the 

 compound microscope first effectively employed by Galileo in 

 1610; and by the middle of the century simple and compound 

 microscopes were being made by opticians in the leading centers of 

 Europe. Significant of the times is the clear appreciation of the 

 importance of studying nature with instruments, which increase 

 the powers of the senses in general and of vision in particular, ex- 

 pressed by Hooke (1635-1703) of London in a remarkable book, 

 the Micrographia, published in 1665. Using his improved com- 

 pound microscope, Hooke clearly observed and figured for the 

 first time the "little boxes or cells" of organic structure, and his 

 use of the word cell is responsible for its application to the proto- 

 plasmic units of modern biology. (Fig. 10.) 



Microscopical work was a mere incident among the varied inter- 



