CHAPTER XV 

 BACTERIA 



No attempt is made here to give even an elementary account of 

 bacteriological technique. Only such phases of the work as are concerned 

 with the immediate microscopical examination of bacteria are touched 

 upon, and these chiefly to afford some practice in this kind of manipula- 

 tion. For special technique, identification, or descriptions of apparatus 

 and accessories, the student is referred to standard textbooks. 



BACTERIAL EXAMINATION 



Bacteria when prepared for microscopical examination are in the 

 form of 



A. Cover-glass preparations, 



B. Bacteria in tissues (section method), or 



C. Hanging-drop preparations. 



A. Cover-Glass Preparations 

 I. Killing and fixing. 



1. From Fluid Media (e. g., bouillon, milk, water, saliva, blood, pus, 

 etc.). Sterilize a platinum wire loop by heating it red hot in a flame. 

 When cool, touch the loop to the culture and spread the adherent 

 bacteria in a thin film over the surface of a cover-glass which has been 

 sterilized in a flame. After the film has dried in the air, kill and fix the 

 bacteria to the cover by passing it three times, film side uppermost, 

 through the apex of a flame. Each time should not exceed half a second. 

 Prepare several films from a given material. Coronet or similar forceps 

 (Figs. 38, 39) should be used for handling such films, because the cover- 

 glass can be left in them through the entire operation of fixing and 

 staining. 



If a platinum loop is not at hand a second cover-glass may be used 

 to spread the smear. The first cover-glass is held in a pair of cover-glass 

 forceps and the second cover-glass is dropped on to it. The glasses are 

 then rapidly drawn apart with a sliding motion by means of forceps. 

 The glasses should not be pressed tightly together. Proficiency in 

 making such preparations is gained only after considerable practice. 

 The chief secret in making a good preparation is to get the films extremely 

 thin and evenly distributed. 



2. From Solid Media (gelatin, agar, meat, potato, animal tissues and 

 organs, etc.). The procedure is the same as for 1, except that a drop of 



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