10 INTRODUCTION 



was the first quantitative physiologic argument. He inferred that there 

 must be small vessels connecting arteries and veins to complete the cir- 

 cular path of the blood but, lacking a microscope, he was unable to see 

 them. In later years he made a careful study of the development of the 

 chick, published in 1G51 as Exercitationes de generatione animaliuni. In 

 this he postulated that mammals, like the chick, develop from an egg. 



The develoj)ment of the compound microscope by the Janssens in 

 1590 and by Galileo in 1(310 provided the means lor attacking many 

 problems in zoology and botany. Robert Hooke (1G35-1703), Marcello 

 Malpighi (1628-1691), Antony van Leeuwenhoek (1632-1723), and Jan 

 Swammerdam (1637-1680) were some of the first microscopists. They 

 studied the fine structure of plant and animal tissues. Hooke was the 

 first to describe the presence of "cells" in jjlant tissue, Leeuwenhoek was 

 the first to describe bacteria, protozoa and sperm, and Malpighi was the 

 first to describe the capillaries connecting arteries with veins. The light 

 microscope has been modified and improved greatly in the past century, 

 and man's ability to see the fine structure of cells has been greatly 

 extended by the invention of the phase microscope and of the electron 

 microscope. The latter, with good resolution at magnifications as great 

 as 80,000 to 100,000 diameters, has revealed a whole new level of com- 

 plexity in the structure of all kinds of cells. 



John Ray (1627-1705) and Linnaeus (Karl von Linne) (1707-1778) 

 brought order into the classification of animals and plants and devised 

 the binomial system (two names, genus and species) for the scientific 

 naming of the kinds of animals and plants. Linnaeus first used this 

 binomial system consistently in the tenth edition of his Systema naturae 

 (1758). 



Contributions to our understanding of the embryonic development 

 of animals were made by Fabricius, the professor of Anatomy at Padua 

 who taught William Harvey, and by Harvey, Malpighi, and Kaspar 

 Wolff (1759). Wolff proposed the theory of epigenesis, an external force 

 that regulated differentiation and development. Karl Ernst von Baer 

 (1792-1876) established the theory of germ layers and emphasized the 

 need for comparative studies of development in different animals. 



Following William Harvey, physiology was advanced by Rene 

 Descartes (1596-1650), who was a philosopher rather than an experi- 

 menter. He believed that "animal spirits" are generated in the heart, 

 stored in the brain, and pass through the nerves to the muscles, causing 

 contraction or relaxation, according to their quantity. Charles Bell 

 (1774-1842) and Francois Magendie (1783-1855) made notable contribu- 

 tions to our understanding of the function of the brain and spinal 

 nerves. Johannes MuUer (1801-1858) studied the properties of nerves 

 and capillaries; his textbook of physiology stimulated a great deal of 

 interest and research in the field. Claude Bernard (1813-1878) was one 

 of the great advocates of experimental physiology, and contributed sig- 

 nificantly to our understanding of the role of the liver, heart, brain and 

 placenta. Henry Bowditch (1840-1911) discovered the "all-or-none" 

 principle of the contraction of heart muscle and established the first 



