lA\()kAl',LK roXDinOXS FOR BACTERIAL (JROWTH 



it forms the basis for the Storcli test for the etiicient}" of the ]);;■- 

 teurization of milk or crean-i for hutter-making. This test is 

 described in the chapter on Pasteurization. 



(2) EnzxTiies developed through the action of genn life — 

 bacteria, }'easts and molds. I'hese are many and \'aried. and 

 cause most of the changes that take place in milk and its products, 

 such, for example, as the ordinar}- souring of milk or cream, and 

 the dexx-lojiment of fla\'or and aroma in cream ripening. 



(;:;) Enz\'mes found in the digestiA'c fluids of animals. All are 

 familiar with the fact that rennet is used in cheese-making. It 

 contains a ferment known as rennin. 



It is the second class of ferments or enzA-mes, the class due to 

 the action ol germ life (principally bacteria), which is of the great- 

 est imp(.>rtance in connection with dairying, anrl wi*h the control 

 of which the dairyman concerns himself most. These ferments 

 are capable of working profound changes, some desirable and S(jme 

 very undesirable. 



Size and Shape of Bacteria. In size, bacteria are the smallest 

 organisms that exist, so far as known. The size varies consider- 

 ably. Russell ' gi^X's the a\-erage diameter as tj-tttitt^)- of an inch. 

 They are so inconcei\'abh- small and light that nine hundred 

 billions of them woukl onl)- weigh 2V of an ounce. - 



Bacteria also var\- considerabh- in shape. They are as a 

 rule classed into three groups: (i) The bacillus or rod-shaped; 

 (2) The coccus or ball-shaped; (,:;) The spirillum or spiral-shaiK-d 

 (like a corkscrew). Some types of bacteria are classified accord- 

 ing to the way in which the_\' arlhere to each other. For instance, 

 when two cocci occur together and form a pair, the\- are called 

 diplococci; when cocci occur in chains, they are called strepto- 

 cocci; when cocci appear in bunches, they are called staphylo- 

 cocci, etc. 



FAVORABLI-; CONUmON.S FOR R.VCTFRI.VL GROWTH 



Food. — Bacteria, like other plants, need food for their exi,=t- 

 ence. The food passes into the bacterial cell in solution, but 

 many (.)rganisms use materials not in solution by producing 



1 Dairv Bacteriology. - Milk, Its N'ature and Composition, by Aikman. 



