Structure, Growth and Distribution. 9 



the twisted or spirillum type (plural spirilla). Most 

 organisms of special significance in dairying belong to 

 the coccus or bacillus group. 



Size of bacteria. The bacteria, as a class, are among 

 the smallest of living objects. None of them are in- 

 dividually visible to the naked eye, and they can be so 

 seen only when clumps or masses are formed in the pro- 

 cess of growth. 



While there is considerable relative variation in size, 

 yet in actual dimensions, this difference is so small as 

 to make careful microscopic determinations necessary. 

 An average diameter may be taken as about one thirty- 



A B C 



FIG. 1. FORMS OF BACTERIA. 

 A, coccus; B, bacillus; C, spirillum. 



thousandth of an inch, while the length varies naturally 

 several fold, depending upon whether the type under 

 observation is a coccus or a bacillus. 



It is very difficult to conceive of the minuteness of the 

 bacteria; the following may give some idea of their size. 

 In a drop of cream ready for churning may be found as 

 many as 10,000,000 and in a piece of fresh cheese as 

 large as a cherry there may be as many living bacteria 

 as there are people on our earth. While the bacteria 

 are very minute, the effect which they exert in milk and 

 other dairy products is great on account of their enor- 

 mous numbers. 



Manner of growth. -The cells of which all plants and 

 animals consist increase in numbers by the division of 



