4 CLEAN MILK 



individuals. The time required for a germ to mature and form a. 

 new germ may not be more than twenty minutes. 



Germs also multiply by spores — that is, small, round or egg- 

 shaped bodies appear within the mature germ and these later- 

 break loose and develop, under favorable circumstances, into full- 

 grown germs again. Germs which increase in this manner are 

 much more difficult to kill, for in the spore stage they often defy 

 prolonged heat, even at the boiling temperature, and also cold at 

 or below freezing and dryness, as dust, in which they may exist for 

 years. To show the possibilities in the way of multiplication, it has 

 been calculated that a single germ, under favorable circumstances,, 

 may within twenty-four hours produce over sixteen millions of 

 progeny. 



Fis- i. 



General shape of bacteria, a, spheres; b, rods; c, spirals. (After Conn.) 



Germs, however, depend upon certain conditions for their 

 growth; otherwise they would crowd all other life off the globe. 

 Besides organic matter to feed on, the chief circumstances limiting 

 their existence are heat and moisture. Germs usually do not grow 

 at a temperature below 39 or above 140 F. This does not apply 

 to the growth of bacteria in ice cream, as germs may multiply five- 

 fold within three days in ice cream kept at a temperature five de- 

 grees below zero Fahrenheit. Milk kept frozen at 29 — 31 ° F., con- 

 taining but a few hundred bacilli to the cubic centimeter at the begin- 

 ning, may contain hundreds of millions of germs when kept in cold 

 storage at this temperature after 5 or 6 weeks (Pennington). The 

 milk at the end of this period is not altered in odor, taste or in any- 

 way to show the tremendous germ-contamination. 



