WHAT ARE BACTERIA? 



two may break apart at once, or each of them may in turn 

 produce other buds before separating; but in either case there 

 are now two cells where there was originally but one. Yeasts 

 also multiply with considerable rapidity, but not, as a rule, as 

 rapidly as many of the bacteria; nevertheless their great power 

 of multiplication makes them of great importance among the 

 forces of nature. The reproduction by budding is the primary 

 characteristic which separates yeasts from bacteria, and the 



FIG. 7 COMMON YEAST 

 Showing multiplication by budding 



FIG. 8 YEAST IN FER- 

 MENTING CIDER 

 Sometimes called "wild 



yeast," coming directly 



from the air 



determination of the method of reproduction will always en- 

 able one to tell whether he has a yeast or a bacterium under 

 study. When, however, one finds under his microscope rather 

 large, round or oval cells, he is pretty safe in concluding that 

 they are yeasts rather than bacteria, and if he can find small 

 cells attached to the larger ones buds he may be absolutely 

 sure that he is dealing with yeasts. 



A second distinction between yeasts and bacteria is in the 

 type of fermentation they produce. Bacteria produce decay, 

 putrefaction and lactic acid fermentation. Yeasts are more 

 commonly associated with the alcoholic fermentation, by which 

 some forms of sugar are easily converted into alcohol and 

 carbon dioxide. The latter type of fermentation does not 

 usually occur in milk. 



The yeasts do not play quite so important a part in dairying 

 as bacteria, and yet, as we shall see later, in some phases of 

 the subject they are of great importance. 



