quite fully discussed since its first descriptions; but no more than 

 two or three of its nearest relatives have at any time been in- 

 cluded with it in the study. 



The parallel treatment attempted in this paper possesses certain 

 points of value; but comparison of a relatively large] number of 

 organisms has its obvious disadvantages as well as its advantages. 

 The number brought under discussion is plainly too great to per- 

 mit, in limited time and space, of extending the work on each 

 germ into detail, or of carrying out all possible tests, chemical, 

 spectroscopic and physiological. But, on the other hand, the com- 

 parison of so many red chromogenic bacteria must throw some 

 light on general features of relationship and variability which are 

 apt to be obscured or lost sight of when attention is concentrated 

 on a single organism or on a small group. 



With these considerations in mind, I have attempted compara- 

 tive study of the following series of forty cultures of red chromo> 

 genie bacilli. A few of these, often referred to in bacteriological 

 literature, have been more or less completely studied as individuals, 

 e. g. B. prodigiosus, B. kiliensis, B. lactis erythro- 

 genes; but the majority, though frequently mentioned, have 

 received only the most cursory descriptions. I have therefore 

 prefixed to my comparative notes a brief description of each 

 "species" here discussed. A list of red chromogenic bacilli not 

 obtainable for study will be found at the close of the paper, where 

 are also tabulated the data regarding my series. 



As an aid in determining the specificity of some members of 

 the series, I obtained from various laboratories eight cultures of 

 B. prodigiosus; the range of variability thus demonstrated for 

 that species and the other parallels or differences between the 

 allied cultures have suggested my closing note on grouping and 

 differentiation. 



Red chromogenic bacilli described in this paper. 

 B. prodigiosus (Ehrenberg) I VIII 



I, from University of Chicago. 



II, from Rush Medical College, Chicago, 1902. 



III, from Board of Health, Chicago, 1902. 



IV, from University of Minnesota, 1903, 



V, from University of Minnesota, 1903. 



VI, from Yale University, 1903. 



VII, from Ontario, Board of Health, 1903. 



VIII, from University of Michigan, 1903. 



'iber 



indie us (Koch) I, from KraTs Laboratorium, 1900. 



i, II O AJMAUMMMIIUIlj -LiTWS. 



II, from Rush Medical College, Chicago, 1902; 

 obtained by them from Parke, Davis & Com- 

 pany, Detroit, 1899, obtained by the latter from 

 the University of Michigan (?) several years before. 



B. ruber plymouthensis (Fiacher) I, from KraTs Laboratorium, 1899. 

 * * II, (B. No. 18), from air at Cold Spring 



Harbor, L. I., I'.iu). 

 III, (II. No. ID), from air at Cold Spring 



HarUr. 

 B. ki liens is (Breunije) from Rush Medical College, Chicago, 1902; obtained by 



them from Parke, Davis & Company, 1&9. 

 B. ruber balticus (Breunig, Kruse) from Krai'* Laboratorium, 1900. 



