EFFECT OF AIR ON MOLD GROWTH 35 



much more rapidly than upon open surfaces. As a result 

 we find that molding is more likely to take place in food 

 when a number of pieces are piled together in a heap, as, 

 for instance, several slices of bread or a number of pieces 

 of fruit. Such a heap furnishes many little recesses 

 partly surrounded by walls which prevent the free pas- 

 sage of air currents, and these little nooks furnish a 

 sheltered place for the mold spores to germinate. If bits 

 of bread are spread out on the shelf of a damp closet they 

 will probably not mold at all, while the same pieces would 

 mold if piled in a heap. Foods with smooth surfaces are, 

 for the same reason, not so liable to mold as those filled 

 with little cavities, like bread. 



On the other hand, molds require some air, and molding 

 almost always begins on the surface. Although, as we 

 have seen, the mold thread can force its way down into 

 the solid substance of food, it always starts upon some sur- 

 face exposed to the air. To grow vigorously, the threads 

 demand an abundance of air, and, as a consequence, will 

 never grow in the center of solid food masses, or at least, 

 if they do, they grow there very slowly. After starting 

 on the surface they may grow for some distance into solid 

 food substance. In the manufacture of Roquefort cheese 

 it is desired that molds should start at the center of a hard 

 cheese mass. To bring this about the growth is stimu- 

 lated by piercing the cheeses full of holes by means of long 

 needles, so that air can penetrate to the center. Air is quite 

 necessary for the formation of the spores, and the fruiting 

 of the mold practically always occurs upon the free surfaces. 

 We need not expect any molding in the center of a mass 

 of food unless some signs of it are visible externally. 



