NOMENCLATURE 317 



that the content of the Brucella group is extremely difficult to define. A.s mentioned 

 already, we have separated the genera Salmonella and Shigella from the more 

 inclusive genus Bacterium. We have combined the genera Erythrobacillus and 

 Chromohacterium under the latter name, since it does not appear to us that the 

 differences in morphology, physiological reactions or habitat between Erythro. 

 prodigiosus and such species as Chr. indicum ruber merit separate generic rank. 

 The final classification of these small saprophytic, chromogenic bacilli must await 

 a more detailed study of the group ; and it seems doubtful whether pigment 

 formation should be accepted as a generic character. We have excluded the 

 genus Erwinia, since the differentiation of coliform organisms of plant origin from 

 those met with in animal tissues seems to rest on no satisfactory basis. 



We append to this chapter a diagrammatic representation (Fig. 47) of the 

 classification given in the final report of the first American Committee (see 

 Buchanan et al. 1928) with the modifications referred to above, noting that we 

 are concerned with the list of genera, rather than with the grouping of these 

 genera into tribes, families or orders. 



We also include in this chapter a summarized description of the characters of 

 each genus, taken from the final report of the first American Committee (Winslow 

 et al. 1920), and emended in some cases in the light of more recent studies of the 

 various groups. 



In the remainder of this book we shall employ these generic names, when 

 referring to any species which appears to be clearly assignable to one of the listed 

 genera. In general, bacteria which can be so assigned are already provided with 

 a specific name, which is not in dispute. Such binomial names will be printed 

 in italic, the generic name being given a capital letter, and used in an abbreviated 

 form. 



Other well-recognized designations for various bacteria will, of course, be freely 

 used, with the recognition that we are using the common name for a particular 

 organism, instead of its scientific name — a practice universally followed in biological 

 science. Such common names will be printed in ordinary type, and without a 

 capital initial letter. For instance, the scientific name of the organism which 

 causes tuberculosis will be written as : Mycobacterium tuberculosis, or more shortly 

 as Myco. tuberculosis, but it will be generally referred to as the tubercle bacillus ; 

 similarly with Corynebacterium diphthericB, C. diphtherice, or the diphtheria bacillus ; 

 Pasteurella pestis, Past, pestis and the plague bacillus ; Brucella abortus, Br. abortus 

 or the bacillus of bovine abortion ; Neisseria gonorrhoecB, N. gonorrhoece or the 

 gonococcus : Streptococcus pneumonice, Str. pneumonicB or the pneumococcus. 



It is a common practice to refer to members of the Streptococcus and Staphylo- 

 coccus groups as streptococci and staphylococci respectively. These terms are 

 colloquial expressions, and we see no reason why a similar use of other generic 

 names in the plural, or of a limited adjectival use of the generic name in the singular, 

 should not be sanctioned. Thus, " the rickettsiae " refers to the members of the 

 genus Rickettsia, " the brucellse " to the members of the genus Brucella, " the 

 pasteurellee " to the members of the genus Pasteurella, and so forth. A salmonella 

 antigen means an antigen met with in one or more members of the Salmonella 

 genus, a proteus type of growth means a growth characteristic of members of the 

 Proteus genus, and so on ; but when the genus is specifically referred to, the adjec- 

 tive should preferably be printed with a capital and in italic, as, for instance, 

 " members of the Salmonella group." The procedure is convenient, the terms 



