CHAPTER IX. 

 THE MICROSCOPE IN MJEDICINE AND SANITATION. 



I. The Microscope in Biology. — ^The microscope bears 

 to biology much the same relation that the balance 

 bears to quantitative chemistry. It is the fundamental 

 instrument without which a true science of living things 

 would be almost impossible. 



The invention of the compound microscope and the 



construction of simple microscopes of high power at 



the middle of the seventeenth century stimulated a dozen 



observers to the study of the finer structures of plants 



and animals. Leeuwenhoek discovered in water and 



in decomposing organic matter a teeming world of minute 



forms of life invisible to the naked eye. Hooke, the 



English botanist, made out the cellular structure of 



plants in his examination of cork. Malpighi and Swam- 



merdam figured the microscopic details of the insect 



body with marvellous patience and success. 



It was only, however, after the perfection of the 



achromatic objective about 1835 that these early labors 



could bear abundant fruit. In 1838-39 Schleiden and 



Schwann developed that great generalization which bears 



their name, the doctrine that all plants and animals are 



104 



