556 Introduction to the Study of Science 



Every housekeeper recognizes the need of unceasing vigilance 

 in guarding against molds in foods and food containers, as 

 pantry, bread boxes, and refrigerator, and is well aware of the 

 promptness with which molds begin to work their undesirable 

 results. 



Favorable conditions. Prevention of molds depends upon 

 knowledge and control of the essential external conditions in 

 which they thrive. These conditions have been suggested in 

 the directions for experiments for mold cultures, but may 

 be summarized briefly. 



The first and most important of the external conditions 

 favorable to the growth of molds and spores when nutritive 

 materials are available is moisture. This must be sufficient 

 not only to dissolve the food materials in a suitable concen- 

 trated solution, but also and especially to keep the cells of the 

 plants full, firm, and turgid. Molds may rest when the moisture 

 is inadequate to growth. 



The second condition is temperature, in adaptation to which 

 molds show remarkable variation. Some species of mold grow 

 slowly, but fully, at a temperature as low as 35 F. Such 

 molds may sometimes be found in refrigerators. Other un- 

 desirable molds flourish best at a temperature ranging from 

 70 F. to 100 F. 



The third condition is light, which is vitally important to 

 chlorophyll-bearing plants, and is also important, but in dif- 

 ferent degree, to molds and fungi generally. Many species 

 of mold can live and grow in bright sunlight, but most do better 

 in darkness, or where the light is subdued. The more common 

 and troublesome species require darkness, partly because this 

 may allow a very slow loss of moisture through evaporation, 

 but chiefly because light is injurious to them and restrictive of 

 their growth. A few species of mold exhibit a remarkable 

 habit of developing all parts of their structure in the darkness, 

 except the reproductive parts, which are formed only in light. 

 But sunlight is generally destructive of molds. 



