SYSTEMATIC CLASSIFICATION 15 



of the method it has been possible to divide the groups still 

 further into serological types so that, for example, Lancefield 

 Group A streptococci have been divided into some thirty- two 

 serological types. 



Animal inoculation 



The medical bacteriologist dealing with pathogenic 

 organisms has a further possibility of characterising an 

 organism by the lesions it produces after inoculation into a 

 suitable animal host. Thus the tubercle organism can be 

 identified by the lesions it produces after injection into a 

 guinea-pig. 



CLASSIFICATION 



By combinations of the tests outHned above it is possible to 

 separate organisms into groups and sub-groups. There will 

 always be individuals which will not fit cleanly into any set 

 grouping, but the majority can be assigned to various pigeon- 

 holes in a systematic classification. In some cases the out- 

 standing characteristics will be morphological, cultural, or 

 pathogenic, while in others differentiation will be based upon 

 finer investigation of a multiplicity of biochemical reactions. 

 Many systems of classification have been used in. the past and 

 there is, unfortunately, no definite agreement upon any one 

 system at the present time. The nomenclature used in this 

 book is that adopted by the Society of American Bacteriologists 

 and detailed in Bergey's Manual of Determinative Bacteriology. 

 In Table I the names of the main Families, Tribes, and Genera 

 used in this book are outlined, but for details concerning the 

 rationale of the classification and for the differentiation of the 

 groups, reference must be made to the Manual and other 

 standard textbooks of bacteriology. - 



ORDERS AND FAMILIES 



The whole group of micro-organisms which come within our 



description of "bacteria" is strictly termed Schizomycetes 



^(fission-fungi) and is divided into several orders. Most 



