142 



BACTERIA, YEASTS, AND MOLDS 



the dry pea or bean. Such a food material is beyond the 

 reach of bacterial action, and, unless these grains become 

 subsequently soaked with water, they are protected from 

 decay (Fig. 62). Bacteria grow in them readily enough in 

 the spring when they are moistened and begin to sprout. 

 This drying of the grains protects all kinds of flours 

 and meals made from them. The wheat is ground into 



flour, and the corn into 

 meal, each of which con- 

 tains but a small amount 

 of moisture, far too little 

 to allow bacteria to feed 

 upon the material. 



RW 1 _-*&^ Flour is P erfe ctly good 



food for bacteria, and if 

 we only moisten it with 

 water, putrefaction and 

 decay begin in a short 

 time; but as it is 

 ordinarily prepared the 

 amount of moisture is too slight for bacteria. The same 

 is true of all flours or meals prepared by grinding dried 

 seeds furnished by plants. To a less extent the same is 

 true of various food preparations made from these flours. 

 In making bread or cake dried flour is mixed with water 

 and subsequently baked. The mixing of the flour with 

 water brings it into a condition for bacterial action, but 

 the baking dries up enough of the water to preserve it. 

 If the baking is so thorough that the water is almost 

 completely driven off, as in the case of dried bisctiits, or 

 crackers as they are called in the United States, the 



FIG. 62. Showing nature's method of 

 preserving seeds by drying. The upper 

 figures are the fresh seed, the lower 

 figures the same after drying for winter 

 preservation. 



