38 BACTERIA, YEASTS, AND MOLDS 



remember that after such heating the food is liable again 

 to receive more mold spores from the air and may there- 

 fore later show another growth of molds. 



Reaction. By reaction is meant the condition of food 

 as to its acidity. Some foods are acid (lemons, pickles), 

 while many may have the opposite reaction, called alkaline. 



The reaction of food is a matter of considerable impor- 

 tance in determining its likelihood to mold. It is true that 

 both alkaline and acid foods may mold, but in general acid 

 foods mold more readily. Lemons are very acid, and so 

 are ordinary fruits, all of which mold very quickly. Molds 

 may even grow upon such strong acid materials as pickles. 

 Bacteria, the second great agent in producing decay, grow 

 in alkaline but not commonly in acid foods. Hence it fol- 

 lows that materials which are most liable to mold are not 

 likely to support the growth of bacteria, and vice versa. 



PRACTICAL SUMMARY 



From these general observations it will be seen that 

 molds will grow best in dark, damp rooms or in corners 

 of the rooms where there is not free circulation of air ; 

 they will flourish in heaps of food where many pieces 

 are massed together ; they will grow vigorously upon food 

 inclosed in jars or boxes, and they prefer darkness rather 

 than light. 



From all these facts we may reach practical sugges- 

 tions as to the methods of avoiding the growth of molds, 

 (i) The most important of all is that food should, so far 

 as possible, be kept tolerably dry. If it is of a nature that 

 will stand drying, it may be protected indefinitely if once 



