Structure of the Bacteria. 9 



many months. Most of the dairy bacteria do not produce 

 spores, and yet in a dry condition, they retain their vitalit}?- 

 unimpaired for considerable periods, if they are not sub- 

 jected to other detrimental influences. 



Light. Bright sunlight exerts on many species a power- 

 ful disinfecting action, a few hours being sufficient to des- 

 troy all cells that are reached by the sun's rays. Even 

 diffused light has a similar effect, although naturally less 

 marked. The active rays in this disinfecting action are 

 those of the chemical or violet end of the spectrum, and 

 not the heat or red rays. 



Influence of chemical substances. A great many chem- 

 ical substances exert a more or less powerful toxic action 

 of various kinds of life. Many of these are of great ser- 

 vice in destroying or holding bacterial growth in check. 

 Those that are toxic and result in the death of the cell are 

 known as disinfectants; those that merely inhibit, or re- 

 tard growth are known as antiseptics. All disinfectants 

 must of necessity be antiseptic in their action, but not all 

 antiseptics are disinfectants even when used in strong 

 doses. Disinfectants have no place in dairy work, except 

 to destroy disease bacteria, or preserve milk for analytical 

 purposes. Corrosive sublimate or potassium bichromate 

 are most frequently used for these purposes. The so-called 

 chemical preservatives used to "keep" milk depend for 

 their effect on the inhibition of bacterial growth. With a 

 substance so violently toxic as formaldehyde (known as 

 formalin, freezene) antiseptic doses are likely to be ex- 

 ceeded. In this country most states prohibit the use of 

 these substances in milk. Their only function in the dairy 

 should be to check fermentative or putrefactive processes 

 and so keep the air free from taints. 



