106 MODERN DAIRY PRACTICE. 



aerobic, i.e., they form first of all in the presence of air. 

 But anaerobic bacteria (i.e., such as cannot live in an at- 

 mosphere containing oxygen) may also be found in milk. 

 The examination of these is unfortunately attended by great 

 difficulties. I have found a butyric-acid fermentation 

 produced by anaerobic bacilli in two samples of milk, and 

 in several other samples have found numerous anaerobic 

 bacteria causing putrefactive fermentations. By an ordi- 

 nary aerobic quantitative analysis only a very few colonies 

 appeared in these samples ; this was contrary to the results 

 of a preceding microscopic examination which showed that 

 the milk was filled with numerous bacteria. The explana- 

 tion of the apparent contradiction was of course that the 

 bacteria found in the milk were largely anaerobic, and 

 could not thus develop in cultures to which the air had 

 free access. 



Other Micro-organisms in Milk. The short enumera- 

 tion of the injurious bacteria of milk given in the preced- 

 ing only includes the bacteria proper. Other micro-organ- 

 isms resembling the bacteria are also found in milk, 

 that may influence its quality. Among these the yeast- 

 fungi may be mentioned. They demand in the main the 

 same conditions of life as the bacteria, are somewhat larger 

 than these, and oval-shaped. They multiply through bud- 

 ding (Fig. 12), i.e., in the manner that cell-buds project 

 from one or both ends of the round cell. This gradually 

 grows until the new cell reaches the size of the mother-cell, 

 when it either breaks off from the latter by a cross- wall, or 

 at once begins to form new buds. 



The yeasts appear comparatively seldom in milk, and 

 only a very few forms are able to cause fermentations in 

 this medium, and thus injure its quality. I have examined 



