CHAPTER VIII. 



MICROSCOPICAL EXAMINATION OF BACTERIA. 



(A) BACTERIA IN LIQUIDS, CULTURES, AND FRESH TISSUES. 



IN conducting bacteriological researches the importance of absolute 

 cleanliness cannot be too strongly insisted upon. All instru- 

 ments, glass vessels, slides, and cover-glasses should be thoroughly 

 cleansed before use. A wide-mouthed glass jar should always be 

 close at hand, containing refuse alcohol for the reception of re- 

 jected slide preparations or dirty cover-glasses. When required 

 again for use, slides can be easily wiped clean with a soft rag. Cover- 

 glasses require further treatment, for, unless they are perfectly 

 clean, it is difficult to avoid the presence of air bubbles when 

 mounting specimens. They should be left in strong acid (hydro- 

 chloric, sulphuric, or nitric) for some hours ; they are then washed, 

 first with water and then with alcohol, and carefully wiped with a 

 soft rag. The same principle applies in the preparation and 

 employment of culture media ; any laxity in the processes of 

 sterilisation, or insufficient attention to minute technical details, 

 will surely be followed with disappointing results by contamination 

 of the cultures, resulting in the loss of much time. 



For the preparation of microscopical specimens it will be found 

 convenient to use a platinum inoculating needle. This consists of 

 two or three inches of platinum wire fused into the end of a glass 

 rod about eight inches in length. Platinum is employed as it 

 rapidly cools after being raised to a white heat in the flame of a 

 Bunsen burner. It is thus completely sterilised, and in a few 

 moments is cool enough not to destroy the bacteria with which it is 

 brought into contact. 



When using platinum needles, either for inoculating fresh tubes 

 in carrying on a series of pure cultures, or in transferring a small 

 portion of a cultivation to a cover- glass for examination under the 

 microscope, the careful sterilisation of the needle by heating the 



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