422 ELEMENTS OF BIOLOGY 



centuries from platform or desk, without any demonstrations or 

 accompanying dissections of the human body. It was not until the 

 sixteenth century that the overthrow of the rule of authority in 

 Biology was accomplished. The independence and originality of 

 Vcsalius (1514-1564) was the pre-eminent influence in this change. 

 Vesalius, attempting to demonstrate human anatomy from the ca- 

 davora by following the descriptions of Galen, frequently found 

 that the description and the facts shown by dissection were at 

 variance. Finally he threw aside his Galen and taught directly from 

 the specimen. 



Biology in the Seventeenth Century. For this and other 

 reasons the science of Biology began to gather impetus. The works 

 of the British physician, William Harvey (1578-1667) mark the next 

 great step in the development of the science, for Harvey added to 

 the age-old method of observation a new method, that of experi- 

 ment. Harvey's best known work is his demonstration that the 

 blood traverses a continuous circuit, but he also made observations 

 and experiments in other fields. His interests were wide and include 

 descriptions of chick and mammalian embryos and speculations 

 as to their origin, focusing attention upon the egg as the origin of 

 all forms. Immediately following the time of Harvey occurred the 

 invention and beginnings of development of the compound micro- 

 scope. As is the case with all successful mechanical devices, the de- 

 velopment of the microscope was not the work of one man but of 

 a number of men; conspicuous among these were Grew and Hooke 

 of England, Malpighi of Italy, and Leeuwenhoek and Schwam- 

 merdam of Holland. Even in its most primitive form this instru- 

 ment opened great vistas for observation and for the revealing of a 

 multitude of facts that in the absence of its powers would always 

 remain unknown or in the realm of conjecture. The rise of modern 

 Biology has accompanied and depended in no small measure on the 

 development of the microscope. When Hooke, in 1665, first de- 

 scribed the cellular appearance of tissues and Leeuwenhoek first 



