CHAPTER V 



CLASSIFICATION OF MICROORGANISMS 



IT is necessary in a consideration of organisms belonging to 

 either the plant or animal kingdoms to divide or separate them 

 into groups, with their apparent relationships as the basis for the 

 grouping. Microorganisms of pathogenic significance we have 

 previously divided into the four groups bacteria, yeasts, molds, 

 and protozoa. A discussion of the classification of the last will 

 be reserved to the chapter on Diseases Produced by Protozoa. 



The classification of micro-organisms is by no means in a satis- 

 factory state. Many bacteriologists and others who have inves- 

 tigated diseases have failed to recognize the importance of simple 

 classifications and have introduced many new names needlessly. 

 It is a principle of nomenclature accepted since the time of Lin- 

 naeus that every plant and animal belonging to a distinct type or 

 species shall receive a Latin name, this name to be made up of two 

 words only. The second of these words is the species name, and 

 is peculiar to the particular kind under consideration, the first is 

 called the genus or generic name. For example, among higher plants 

 we have the genus Quercus, or oak, which is subdivided into many 

 species, such as white oak, red oak, swamp oak, etc. (Quercus alba, 

 rubra, etc.) . The generic name is applied to all those species which 

 resemble each other, as do all of the oaks. Species of plants and ani- 

 mals are given names which are understood to serve as convenient 

 terms for their designation. It is an established principle that the 

 name first given to a plant or an animal is the one which should 

 always be used whenever that name is in accordance with certain 

 rules. Some bacteriologists have made the mistake of believing 

 that a scientific name should be a description or even a descriptive 

 term. It is no more necessary that the species name of a bacterium 

 should describe that bacterium than that the given or Christian 

 name of an individual should describe him. Disregard of this rule 

 has resulted in some very unwieldy names being given to micro- 



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