384 APPLIED PHYSIOLOGY 



mold which grows in the human skin. Mildew and toad- 

 stools belong to the same family as molds. In nature 

 molds disintegrate, and return to the soil and air all kinds 

 of dead plant and animal substances, especially hard and 

 resisting tissues like bones, tree trunks, and skins, so that 

 they can again become available as plant food. In warm, 

 humid weather molds grow readily and are often destruc- 

 tive to food and clothing. 



684. Bacteria. The smallest and simplest, as well as 

 the most numerous of living creatures, are round or rod- 

 shaped bodies from 2TTro Q" to Tiroinr ^ an ^ nc ^ m breadth, 

 and seldom more than ysV^ of an inch in length. They 

 are sometimes called microbes, but more common names 

 are bacteria or germs. They are all plants whose mode of 

 growth somewhat resembles the yeasts and molds. Like 

 yeast and mold they, or their spores, are scattered every- 

 where in the air. When they fall upon moist albumin they 

 grow. A single one can produce over 10,000,000 in the 

 course of twenty-four hours. They often resist influences 

 which would destroy most other forms of life. Even boiling 

 for five minutes fails to destroy the spores of some. 



685. Effects of bacteria. Bacteria destroy the substances 

 in which they grow. Most forms of decay are due to the 

 action of certain varieties of bacteria. They cause dead 

 matter to become soft and melt away, usually with the 

 production of foul-smelling gases and a variety of poison- 

 ous ptomaines. In the soil there are forms of bacteria 

 which oxidize all kinds of animal and vegetable albumin 

 as thoroughly as though it were burned. Thus bacteria 

 destroy the dead and waste matter of vegetables and ani- 

 mals and prepare it for vegetable food again. Yeast, mold, 

 and bacteria are indispensable friends of all living beings ; 

 and decay is a step in the preparation of our food. 



