10 PRINCIPLES OF ANIMAL BIOLOGY 



The Microscope. — One important aid to the mechanistic theory of 

 living matter was the invention of the compound microscope. The 

 refractive power of glass had long been known, and simple lenses had 

 come to be used in the sixteenth century for spectacles and as scientific 

 toys. The combination of two or more lenses in a tube to form a com- 

 pound microscope is generally attributed to Zacharias Jensen and is 

 said to have been first used about the year 1591. During the following 

 century considerable improvement of these instruments was effected. An 

 early microscopist, Robert Hooke (page 15), described the one at the 



Fig. 6. — Marcello Malpighi, 1628-1694. {From Garrison, ''History of Medicine," after the 



painting by Tabor, Royal Society.) 



left in Fig. 5, while a moderately improved one is on the right. Almost 

 no further improvement was made thereafter for a century and a half. 



The founder of microscopic anatomy was Marcello Malpighi (1628- 

 1694), of Italy (Fig. 6). He studied the lungs and observed the capil- 

 laries, thus confirming the theory that blood circulates through them. 

 He also examined various glands, the embryo of the chick, the structure 

 of the silkworm, and the tissues of plants. His work on plants was 

 extensive, and, with Nehemiah Grew (1628-1712) of England, he became 

 the founder of plant anatomy. Anton van Leeuwenhoek (1632-1723) 

 (Fig. 7), of Holland, stepped out from behind his dry goods and notion 

 counter often enoiigli to become one of the most skillful of the makers of 

 lenses; one of his lenses, still in existence, magnifies two hundred and 

 seventy times. He made these for his own use, never sold one, and never 



