CHAPTER III. 



MICROSCOPIC METHODS GENERAL BAC- 

 TERIOLOGICAL DIAGNOSIS INOCULATION 

 OF ANIMALS. 



The Microscope. For ordinary bacteriological work a 

 good microscope is essential. It ought to have a heavy 

 stand, with rack and pinion and fine adjustment, a double 

 mirror (flat on one side, concave on the other), a good 

 condenser, with an iris diaphragm, and a triple nose-piece. 

 It is best to have three objectives, either Zeiss A, D, and T \- 

 inch oil immersion, or the lenses of other makers corre- 

 sponding to these. The oil immersion lens is essential. 

 It is well to have two eye-pieces, say Nos. 2 and 4 of Zeiss 

 or lenses of corresponding strengths. The student must 

 be thoroughly familiar with the focusing of the light on the 

 lens by means of the condenser, and also with the use of the 

 immersion lens. It may here be remarked that when it is 

 desired to bring out in sharp relief the margins of unstained 

 objects, e.g., living bacteria in a fluid, a narrow aperture 

 of the diaphragm should be used, whereas, in the case of 

 stained bacteria, when a pure colour picture is desired, the 

 diaphragm ought to be widely opened. The flat side of 

 the mirror ought to be used along with the condenser. 

 When the observer has finished for the time being with his 

 immersion lens he ought to wipe off the oil with a piece of 

 silk or very fine washed linen. If the oil has dried on the 

 lens it may be moistened with xylol never with alcohol, 



