PART I. 

 BACTERIOLOGICAL TECHNIC 



CHAPTER I. 

 THE MICROSCOPE AND MICROSCOPIC METHODS. 



The development of bacteriology has depended especially 

 upon the development of new methods of scientific study, and 

 in a very important way upon the improvements in construction 

 of the microscope and in methods of preparing objects for study 

 under the microscope. Knowledge of the construction of a mi- 

 croscope is not an essential part of bacteriology but the demands 

 of modern microscopical methods require a skill in manipulation 

 of the instrument which is best acquired after the principal struc- 

 tural features of the microscope are understood. 



The Development of the Microscope. Roger Bacon, in 

 1276, seems to have been the first to recognize the peculiar prop- 

 erties of a lens. Spectacles began to be used about the same 

 time and are said to have been invented by d'Armato. 1 Gali- 

 leo (1610) probably made the first record of the use of the com- 

 pound microscope. It was a lens maker, Anton van Leeuwen- 

 hoek, who first saw bacteria in 1683. A method of correcting 

 chromatic aberration was discovered by Marzoli in 1811, but 

 became generally known through the work of Chevalier in 1825. 

 The correction of the color defects was accomplished by the com- 

 bination of two kinds of glass, crown glass and flint glass, in the 

 1 Jour. A. M. A., Nov. 9, 1912, Vol. LIX, p. 1721. 



