112 BACTERIA, YEASTS, AND MOLDS 



measure, protected from spoiling, since the bacteria are 

 mostly killed. But if the food is simply warmed, the 

 spoiling is hastened instead of delayed. For example, 

 in making beef tea, if the liquid is boiled, it will keep 

 easily; but since boiling precipitates the proteids and 

 deprives the material of most of its food value, it is better 

 to make it by warming without boiling. Such material 

 decays very rapidly, and, if set on the back of the stove to 

 keep warm, will be spoiled in a short time. Moderate heat 

 hastens bacteria growth. Boiling kills all but spores. 



Light. Direct sunlight rapidly kills bacteria (except 

 some spores) and daylight in general has an injurious 

 effect upon them in proportion to its intensity. They 

 grow best in darkness. Dust or dirt exposed to sun- 

 light soon loses most of its living bacteria, while in dark 

 cellars, dark corners, and cracks they may remain alive a 

 long time. Hence the rooms in our houses should be 

 kept light. The too frequent habit of closing blinds and 

 using heavy curtains or shutters to keep out the light 

 is a great mistake. Pantries and kitchens should have 

 all the light possible. A sick room particularly should 

 have all possible sunlight ; and bright colors for wall 

 paper, curtains, etc., will aid not only in making it cheer- 

 ful but in actually destroying the disease bacteria. Sun- 

 light and fresh air should everywhere take the place of 

 the darkened, closed rooms which have been only too 

 common in our houses in past years. 



Relation to Air. Most living things require oxygen 

 and therefore demand air for their growth. This is true 

 of a majority of bacteria. Most bacteria like to feed 

 where they can have plenty of air. Hence decay is apt 



