MICROSCOPE 29 



CHAPTER II 

 BACTERIOLOGICAL APPARATUS 



The Microscope. A microscope for bacteriological work 

 should be absolutely rigid, and the fine adjustment 

 should be sensitive and precise. It must be fitted with 

 a suitable substage condenser, with an arrangement for 

 focussing, and iris diaphragm. A triple nose-piece avoids 

 unscrewing the objectives to obtain variations in power, 

 and saves not only time, but much wear and tear. 

 The following objectives are required: |-inch, ^-inch, 

 and a j^-inch oil immersion. These objectives com- 

 bined with an ' A ' or ' B ' eye-piece will give magnifi- 

 cations to 1,100 diameters, which is ample for all ordinary 

 purposes. 



A mechanical stage of an easily detachable form is 

 desirable, especially for the systematic examination of 

 blood-films, etc. 



A brilliant illumination is essential for the examination 

 of bacteria, particularly when in tissues. A paraffin lamp 

 with flat flame, the edge of the flame being used, is very 

 satisfactory; or, if electric current be available, a Nernst 

 lamp enclosed in a frosted globe, or the Barnard lamp. 

 Daylight is not always suitable, but it is as well to be able 

 to use it on occasion. 



Micro-organisms in liquids and tissues are only visible 

 through the shadows caused by the differences in the 

 refractive power of the various structures. Consequently 

 the hole in the diaphragm must be diminished. In the 

 case of stained specimens, however, an open diaphragm 

 can be used, and the preparation examined with the full 

 aperture of the condenser. 



After using the oil-immersion objective, the cedar oil 

 should be removed with soft filter-paper and the lens then 

 wiped with a silk handkerchief. Should the oil be allowed 

 to dry on at any time, a little fresh oil should be put over 

 it and allowed to stand a short time; this will soften the 

 hardened oil, when the whole may be cleaned off together, 

 or it may be gently cleaned with a rag moistened with 

 xylol. 



