BACTERIOLOGICAL TECHNIQUE 



15 



IV. GENERAL METHODS OF BACTERIOLOGICAL 

 INVESTIGATION. 



THE MICROSCOPE. 



For bacteriological investigation, a modern microscope with an 

 Abbe condenser, iris diaphragm, and low and high power lenses, is 

 necessary. The following makers can be selected from : 



ZEISS. 



Objective AA. 

 DD. 



Homogenous Immersion, one-twelfth. 

 Eye-pieces II. and IV. 



LEITZ. 



Objective III. 

 VII. 



Homogenous Immersion, one-twelfth. 

 Eye-pieces I. and III. 



The low power is used with a narrow diaphragm for the examina- 

 tion of colonies of bacteria developed on plate or Petri dish cultures. 



Unstained specimens are always examined with a narrow diaphragm, 

 whilst for stained specimens an open diaphragm is necessary. In 

 examining double-stained sections an open diaphragm is used for the 

 bacteria and a narrow diaphragm for the tissue. The oil immersion 

 lens after use must be cleaned with benzine and wiped with a 

 chamois skin or special lens paper. Excess of immersion oil is 

 removed from the cover-glass with xylol, which can also be used in- 

 stead of benzine for cleaning the lenses. 



V. METHODS OF PREPARING COVER-GLASS 

 SPECIMENS. 



FLUIDS. 



The platinum loop, previously sterilized in the Bunsen flame, is used 

 to transfer fluids to the cover-glass. 



SEMI-SOLID MATERIAL. 



A drop of sterile water is placed on a cover-glass and the material 

 mixed with the water by means of a sterilized platinum wire or loop. 



TISSUES, PIECES OF ORGANS, ETC. 



Portions of the material are spread on the cover-glass with a 

 sterilized platinum wire, or the cover-glass is drawn quickly across 

 the cut surface of the tissue or organ. 



