CLASSIFICATION 39 



is very confusing, could not well have been avoided in the 

 earlier stages of descriptive bacteriological work and before 

 differential media were employed. There are, however, 

 many species which possess well denned properties or patho- 

 genic powers by which they can be positively identified. 



In analysing a substance like milk or sewage one en- 

 counters many bacteria that are very difficult to identify by 

 comparing the description of their cultural characters with 

 the very brief identifying descriptions recorded in the sev- 

 eral manuals 1 that have been written for this purpose. 



In order to bring about a more uniform description of 

 species for purposes of records and identification the Society 

 of American Bacteriologists have recommended a chart for 

 recording descriptions of the growth and morphology of 

 bacteria and a decimal system for grouping species or varie- 

 ties. This chart is very helpful in recording descriptions for 

 subsequent reference. 



There are many bacteria that resemble well defined 

 species so closely that they must be considered varieties of 

 it. Such species and their varieties are frequently referred 

 to as a group, such for example as the "colon group." In 

 most quantitative analyses no attempt is made to identify the 

 species, other than well defined and important ones, beyond 

 the placing of them in the group to which they belong. 



The procedure to follow in identifying species is first 

 to determine the morphology and the cultural and bio-chemic 

 properties and pathogenesis of the organism in question and 

 then to compare them by the use of manuals or other litera- 

 ture with the descriptions of the species already described 

 and named. If the organism can not be identified it may 

 be placed, temporarily at least, in some group of bacteria or 

 if in the judgment of the worker it is sufficiently distinct it 

 may be recorded and named as a new species. 



1 Chester, A Manual of determinative Bacteriology. 



2 Fluegge, Die Mikroorganismen. 



3 T. Matzuschita, Bacteriologische Diagnostik. 



4 Migula, System der Bakterien. 



