THE ROLE OF MICROORGANISMS 5 



same kind of food as dot's the animal; their food must sup- 

 ply them with both building materials and energy. The 

 term "/"".'/>" or "/"".'/"* l>l"tx" is applied to them. One 

 dors not think of the animals as agents in the destruction 

 of organic matter, for our interest in them is wholly along 

 other lines. The waste products of animal life are very 

 simple chemical compounds. Some of the fungus plants 

 change their food relatively little as far as its chemical 

 complexity and energy content is concerned. Their by- 

 products are almost as complex as is the food itself, and in 

 many instances possess economic value. 



The destructive work of animals and of the fungus plants 

 is included under the term decomposition. Other terms, 

 such as fmiH-nttitiun, d<c<uj, putrefaction, and rotting, are 

 synonymous. Usually, however, these expressions are ap- 

 plied to the decomposition of certain chemical substances, 

 or to a particular type of decomposition; for example, one 

 says that milk ferments and that meats putrefy. 



The greater part of the decomposition of organic matter 

 is occasioned by fungus plants of microscopic size that find 

 their home in the soil and in the water. The body of an 

 animal is buried; within a short time it completely disap- 

 pears. An immense amount of waste organic matter may 

 be placed in a stream as, for example, in the great drain- 

 age canal that receives the sewage of Chicago. Before the 

 stream that receives the effluent of the drainage canal 

 reaches central Illinois, the organic matter has completely 

 disappeared under the influence of the microscopic life of 

 the water. 



From this organic matter are formed carbon-dioxide, 

 water, sulphates, phosphates, and nitrates. From organic 

 matter minerals have been formed; therefore the term 

 mineralization is often applied to the process. An element 

 passes from the soil, the water, or the air into the green 



