INTRODUCTION 9 



and where they lived, which are remarkable mixtures of fact and fiction. 

 Some of the ones written in the Middle Ages were called "bestiaries." 

 The zoological books written in the Middle Ages are, almost without 

 exception, copied from Aristotle, Galen and Pliny; no original observa- 

 tions were made to corroborate or refute the accuracy of these 

 authorities. 



The Renaissance in science began slowly with scholars such as Roger 

 Bacon (1214-1294) and Albertus Magnus (1206-1280) who were inter- 

 ested in all branches of natural science and philosophy. The genius 

 Leonardo da Vinci (1452-1519) was an anatomist and physiologist as 

 well as a painter, engineer and inventor. He made many original 

 observations in zoology, some of which came to light only much later, 

 when his notebooks were deciphered. 



One of the first to question the authority of Galen's descriptions 

 of human anatomy was the Belgian, Andreas Vesalius (1514-1564), who 

 was professor at the University of Padua in Italy. By actual dissections 

 and by making detailed, clear drawings of what he saw, Vesalius re- 

 vealed many of the inaccuracies in Galen's descriptions of the human 

 body. He published his observations and illustrations in De Humani 

 corporis fabrica (On the Structure of the Human Body) in 1543. Since 

 Vesalius dared to reject the authority of Galen, he was the object of 

 much adverse criticism and was finally forced to leave his professorial 

 post. 



Just as Vesalius had emphasized the importance of relying on 

 original observation rather than on authority in anatomy, so did Wil- 

 liam Harvey (1578-1657) in physiology. Harvey was an English physician 

 who received his medical training at the University of Padua, where 

 Vesalius had taught. He returned to England and investigated the 

 circulation of the blood. In 1628 he published Exercitatio anatomica de 

 motu cordis et sangiii)iis in anuiialibus (Anatomical studies on the mo- 

 tion of the heart and blood in animals). At that time blood was believed 

 to be generated in the liver from food and to pass just once to the 

 organs of the body where it was used up. The heart was believed to be 

 nonmuscular and to be expanded passively by the inflowing blood. 

 Harvey described, from direct observations on animals, how first the 

 atria (auricles) and then the ventricles fill and empty by muscular con- 

 traction. He showed by experiment that when an artery is cut blood 

 spurts from it in rhythm with the beating of the heart, and that when 

 a vein is clamped it becomes full of blood on the side away from the 

 heart and empty on the side toward the heart. He demonstrated that 

 the valves in the veins permit blood to flow toward the heart but not in 

 the reverse direction. From these experiments he concluded that blood 

 is carried away from the heart in arteries and back to the heart in veins. 

 Furthermore, by measuring how much blood is delivered by each beat 

 of the heart, and by measuring the number of heartbeats per minute, he 

 could calculate the total flow of blood through the heart per minute or 

 hour. This he found to be so great that it could not be generated anew 

 in the liver but must be recirculated, used over and over again. This 



