HISTORY OF ZOOLOGY 



653 



zoological progress. People were content to 

 rely on the work of Aristotle and other an- 

 cient philosophers which was often distorted 

 beyond recognition. The struggle out of this 

 distressing situation was difficult and did not 

 succeed until the sixteenth century. 



Andreas Vesalius (1514-1564) and Wil- 

 liam Harvey (1578-1657) were leaders in 

 the revival of zoological investigation. Ve- 

 salius (Fig. 456) was a Belgian anatomist 

 who in 1543 published a large treatise. On 

 the Structure of the Human Body. This 

 work is of particular importance since data 

 contained in it were obtained by direct ob- 

 servation. To Vesalius, zoolog}- owes the 

 overthrow of reliance on authority. 



Figure 456. Andreas Vesalius (1514-1564), the 

 Belgian anatomist, who placed human anatomy on 

 a firm basis of exact observation. 



William Harvey (Fig. 457) was an Eng- 

 lish physician who published in 1628 an 

 epoch-making monograph, On the Motion 

 of the Heart and Blood in Animals. This 

 book was a pioneering expression of the 

 scientific method. Harvey was able to dem- 



onstrate that the blood circulates through 

 the body, being forced out of the heart and 

 returning again to the heart. This work 

 threw an entirely new light on the subject 

 of physiolog)' in general and had tremendous 

 influence on the progress of zoology, since 

 it transformed it into an experimental sci- 

 ence. 



Figure 457. William Harvey (1578-1657), the 

 English physician, who, in 1628, was the first to 

 demonstrate by experiment the circulation of the 

 blood. 



The discover}' of the compound micro- 

 scope early in the seventeenth century 

 opened a new field for investigation and led 

 to the remarkable work of Robert Hooke 

 (1635-1703), an English scientist, to whom 

 we owe the word cell; and to that of van 

 Leeuwenhoek (1632-1723), a Dutch micro- 

 scopist, who discovered bacteria and proto- 

 zoans. Although spermatozoa were first 

 observed by Hamm, another Dutchman, 

 Leeuwenhoek studied the sperms of many 

 animals. The microscope also enabled Mal- 

 pighi (1628-1694), an Italian histologist, 

 to place the subject on a firm basis. Hooka's 

 Micrographia was published in 1665. 



