MICRO-ORGANISMS AND ENZYMS 



287 



several classes; but those of greatest interest in con- 

 nection with cheddar cheese-making are called bac- 

 teria. These are the smallest conceivable forms of 

 plant life. Each individual consists of a single cell, 

 averaging in diameter one-thirty-thousandth of an 

 inch. 



(i) Kinds. — Bacteria appear in three general 

 varieties of form: (a) Ball (coccus), (b) short rod 

 (bacillus), and (c) corkscrew (spirillum). (Figs. 

 39-42.) 



FIG. 39 — BALL-SHAPED BAC- 

 TERIA (coccus). 



(Rogers) 



FIG. 40 — CHAINS OF BALL- 

 SHAPED (coccus) BAC- 

 TERIA 



(Rogers) 



(2) Method of grozvth and reproduction. — They 

 multiply in number, or reproduce, by simple division ; 

 that is, when a cell grows in size, it increases more 

 in one direction, so as to result in lengthening out 

 slightly, and a partition forms across the cell, thus 

 producing two new cells in place of the old one ; and 

 then each of these subdivides again and so on con- 

 tinuously. Some kinds of bacteria form spores in 

 the cells; these are to bacteria what seeds are to 



