CLASSIFICATION OF MICROORGANISMS 31 



kinds of plants which botanists agree must be separated 

 into several divisions. Some of the so-called molds really 

 belong to the higher fungi. But though the term "mold" 

 is not a good scientific one, practically it is very useful. 

 It is a common English word, quite generally understood, 

 and always refers to a variety of plants characterized 

 by a general appearance so well known as to be easily 

 recognized by persons who are entirely unfamiliar with 

 scientific botany. Although admitting that the molds do 

 not represent any real scientific division of fungi, we may 

 use the term as referring to colorless plants which every 

 one recognizes but which cannot be scientifically defined. 



The other two groups, jreasts and bacteria, are proper 

 scientific divisions. 



In our study of household problems we are concerned 

 only with molds, yeasts, and bacteria. 



Protozoa 



One or two diseases referred to in later chapters are 

 caused by animals rather than plants. Malaria is certainly 

 so caused, and possibly smallpox. These animals are uni- 

 cellular and belong to the group Protozoa. 



