Structure, Growth and Distribution. 17 



must of necessity be antiseptic in their action, but not 

 all antiseptics are disinfectants, even when used in large 

 amounts. Disinfectants have no place in dairy work, 

 except to destroy disease-producing bacteria, or to pre- 

 serve milk for analytical purposes. The so-called chem- 

 ical preservatives used to "keep" milk depend for their 

 effect on the inhibition of bacterial growth. In this 

 country, most states prohibit the use of these substances 

 in milk. Their only function in the dairy should be to 

 check fermentative and putrefactive processes outside 

 of milk and so keep the air free from taints. 



Products of growth. All bacteria, as a result of their 

 growth in food substances, form more or less character- 

 istic compounds that are known as by-products. The 

 changes brought about are those of decomposition and 

 are collectively known as fermentations; they are char- 

 acterized by the production of a large amount of by- 

 products as the result of the development of a relatively 

 small amount of cell life. The souring of milk, the rot- 

 ting of eggs, the spoiling of meats, the making of vine- 

 gar from cider are examples of fermentations caused by 

 different bacteria. 



If the substances decomposed contain but little sugar, 

 as do animal tissues, the conditions are favorable for the 

 growth of the putrefactive bacteria, and foul-smelling 

 gases are formed. When sugars are present, as in milk, 

 the environmental conditions are most favorable for the 

 acid-forming bacteria that do not as a rule produce of- 

 fensive odors. 



Many of the bacteria form substances known as en- 

 zymes which are able to produce certain decomposition 

 changes in the absence of the living cells, and it is by 

 virtue of these enzymes that the organisms are able to 

 2 



