Microorganisms in Relation to Man 555 



molds of different varieties. A certain species infests the roots 

 of many vegetables, such as cabbage and turnip, causing the 

 familiar disease known as clubroot, in which the root is dis- 

 torted and swollen in a peculiar way. 



276. Distribution. Molds are adapted through their spores 

 to universal distribution by moving air, dust, water, or any 

 object on earth. They make any place their habitat, such as 

 factory, store, and home, where they cause trouble and perhaps 

 loss for all concerned. Hardly any place in the home is exempt. 

 Evidence of their presence is sometimes found in basement and 

 attic, closets, pantries, and refrigerators. One may easily dis- 

 cover whether or not mold spores are present in any place by 

 exposing for a while pieces of moistened bread, fruit, meat, or 

 cheese. Even damp cloth, leather, and wood furnish nutri- 

 ment for molds. Mildew is a mold which grows on any of these 

 materials that are sufficiently moist and warm. 



277. Their vitality. Molds and spores are also capable of 

 resisting successfully many extreme conditions in nature. The 

 spores are very dry, and remain uninjured by prolonged drought, 

 or excessive moisture. They are not impaired when subjected 

 to such extremes of temperature as occur in nature. Indeed, 

 spores withstand a temperature that approaches closely the 

 boiling point of water. It is usually supposed that they are 

 destroyed by being boiled in water. Spores have been cooled 

 to extremely low temperatures, just a few degrees above ab- 

 solute zero ( 459 F., 273 C.), and suffered no injury. 

 Thus molds through their spores are adapted to survive and 

 retain their vitality indefinitely in practically every combina- 

 tion of conditions in the natural environment. 



278. Their rate of growth. Molds vary in their rate of 

 growth and fruition. Some grow very rapidly, completing 

 their life cycle within twenty-four hours. Though common 

 experience is often a good witness to the speed with which 

 mold spores germinate and secure strong foothold in food ma- 

 terials, you may verify this by experiment and observation. 



