BACTERIA AND THEIR RELATION TO DAIRYING. 13 



Three methods are generally used in the study of bac- 

 teria, viz.: (a) microscopic examination; (b) culture of the 

 bacteria on different nutritive substrata; and (c) inocula- 

 tion experiments with animals. As we are here dealing 

 especially with non-pathogenic bacteria, we shall only 

 dwell on the first two methods, since inoculation is only 

 used in the study of pathogenic bacteria. 



a. Microscopic Examination. In applying the first 

 method, a compound microscope is essential. This ought 

 to magnify at least 500 times, and preferably more. With 

 such an instrument the presence of bacteria can be directly 

 proved in several liquids, as in case of slops from creamery- 

 gutters, standing liquid-manure pools, etc. In other liq- 

 uids and in mediums where the bacteria present either ap- 

 pear in smaller numbers or are extremely small or are 

 hidden by other bodies (as in the cream and milk) they 

 cannot be observed in this easy manner. In such cases 

 the bacteria must be stained, an operation usually per- 

 formed by means of different anilin colors, and they will 

 then appear plainly when seen through a microscope. 

 Although this method in many instances will lead to im- 

 portant observations, it seldom gives decisive results as 

 regards the question of the characteristics of single species. 

 The bacteria are extremely simple organisms, which offer 



KRAMER. Die Bakteriologie in ihren Beziehung zur Landwirt- 



schaft, Wien, 1892. 

 FREUDENREICH. Bakteriologie in der Milchwirtschaft. Basel, 



1893. 



GfJNTHER. Bakteriologie. Leipzig, 1890. 

 CONN. The Fermentations of Milk. Washington, 1892. 

 WEIGMANN. Die Methoden der Milchconservirung. Bremen, 



1893. W. 



