126 BACTERIA, YEASTS, AND MOLDS 



THE EFFECT OF BACTERIAL GROWTH UPON FOOD 



If any common food product is sufficiently moist, bac- 

 teria which get into it from some source are sure to grow 

 and in the course of a few hours will produce marked 

 changes therein. But bacteria do not consume food as 

 large animals do by taking it bodily inside of themselves. 

 They are quite too small to do this. To the eye it does not 

 seem that the bacteria are actually consuming the food 

 but that they are simply producing noticeable changes 

 within it. In reality, however, they are consuming it 

 and in the end cause its almost complete disappearance. 

 The essential effect that they produce is the chemical 

 decomposition of the material upon which they are feed- 

 ing. Bacteria do not consume the whole food but use 

 only a part of it. An illustration may make clear their 

 mode of action. If a house is built with a wooden 

 frame and brick walls, and the wood is burned away, the 

 house is sure to tumble to pieces, because the wooden 

 framework is necessary to hold the building together. 

 Much the same thing is true of a chemical molecule, which 

 is a structure made of a variety of substances bound 

 together to form a unit. Bacteria, as they utilize foods, 

 have the power of taking some of these materials out of 

 the molecule, but cannot consume the whole. The result 

 of extracting some of the material from a molecule is that 

 the entire structure will fall to pieces, just as the house 

 falls whose framework has been burned away. The meat 

 becomes putrid, the milk sours, the egg rots, and any 

 other material containing proteid undergoes a similar type 

 of spoiling. 



