CHAPTER IV. 



METHODS OF STUDYING MICROORGANISMS- 

 STERILIZATION BY HEAT. 



LABORATORY TECHNIC. 



IN the study of microscopic beings it has been necessary 

 to elaborate a special technic which will supply the require- 

 ments of life. Before the epoch-making work of Koch it was 

 necessary to cultivate microorganisms upon broth or bread, 

 and there was little known as to the exact composition of the 

 medium. Koch showed how to control the growth of bacteria 

 in the laboratory. To Pasteur and Kohn credit also is due 

 for the standardizing of the foodstuffs upon which bacteria 

 are cultivated. Let us assume that we have been given a 

 culture of bacteria to study. Since the identification of 

 species is not a part of a nurse's duty it is not necessary to 

 discuss the separation of many germs in a mixture. Bacteria 

 are transferred from one place to another, as, for example, 

 from one culture tube to another or to a glass slide, by means 

 of a piece of platinum wire set into a handle. This metal 

 will withstand great heat and can be sterilized in the flame 

 of a Bunsen burner after every using. The Bunsen burner 

 is an apparatus so arranged that air is thoroughly mixed 

 with the gas and the mixture is completely burned. Starting 

 out with the material from which this single organism comes, 

 the bacteriologist spreads it on a glass slide and colors it by 

 certain aniline or vegetable dyes, of which there is a large 

 number. It is practically impossible to identify certainly 

 any bacterium by a simple examination of a stained prepara- 

 tion under the microscope. The observer, however, does 



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