268 LABORATORY EXERCISES IN BACTERIOLOGY. 



(E) Subfamily: CHROMATIACE^. 



(a) Genus: Chromatium. 



(b) Genus: Rhabdochromatium. 



(c) Genus: Thiospirillum. 



In the study of any unknown bacterium the student should have in his possession 

 all the data which are obtained in a systematic completion of some blank form as 

 provided in the Appendix of this volume. Furnished with this information, the 

 identification may be attempted by reference to the analytic keys in various systematic 

 works on bacteriology (Chester, Migula, Neumann and Lehmann, Sternberg, Fliigge, 

 Hueppe, Fischer, Mace, et a/.). In case of typical forms the recognition by such refer- 

 ence is not a matter of great difficulty; but, unfortunately, owing both to the insuffi- 

 ciency of our knowledge arising from inefficiency of methods of demonstration, faults 

 of description of many species, and consequent confusion of system, and to the greater 

 or less variability apt to be met in a given species, difficulties do arise for the experi- 

 enced as well as the inexperienced. Patience and care of observation are absolute 

 essentials. As far as they go, our methods, if properly applied, are reliable, and when 

 in difficulty the student should recall the possibility of bacterial variation as giving 

 rise to his trouble and extend his observations to other examples of the species under 

 investigation, in hope of detecting the source of apparent discrepancy. Methodical, 

 painstaking effort will always yield some measure of success ; and if certain recognition 

 of the species is impossible to the student, at least it will be possible to refer temporarily 

 and tentatively the bacterium studied to some class typified by some well-known 

 organism, after which the subsequent work is narrowed to differentiation from the 

 other members of the same class. 



The scope of this work scarcely permits the publication of any extended analytic 

 key, for which reference to the descriptive texts must be made; however, for con- 

 venience in the preliminary classification, the following outline, based upon the above 

 table of classification, and adapted with some changes from Chester's Determinative 

 Bacteriology, is presented, leading to the separation into genera of the true bacteria. 

 Thereafter follows a list of equivalents of the generic names to which reference may 

 .be made in the use of reference works other than Chester in the determination of 

 species. 



(A) Cell contents devoid of bacteriopurpurin or 

 sulphur granules, red or violet. (Chester 

 recognizes among this group a few forms as 

 thiospirillum, thiothrix, and a class of pseudo- 

 monads which contain sulphur granules, which 

 in the above table of classification are, however, 



placed among the thiobacteriacese), EUBACTERIACE^. 



I. Cells globular, free or united, usually non- . 



motile, mostly without flagella, Family: Coccaceae. 



(a) Cells without flagella; division in one plane 



(cells united in one direction) , Genus : Streptococcus. 



(b) Cells without flagella; division in one, two, 

 or three planes to formation of individuals, 

 merismopedia or zooglea masses, Genus: Micrococcus. 



