70 SULPHUR BACTERIA 



investigation to ascertain to which of these genera any particular 

 organism belongs. The author is of the opinion that no 

 difference exists between the genera Sarcina and Micro- 

 coccus. An organism is generally ascribed to Sarcina if 

 observed dividing in three dimensions, and to Micrococcus 

 if in two dimensions, but it has been shown that the same 

 organism may use both methods of division. It is an easy 

 matter, by subculture, to effect the transformation of a 

 Sarcina into a typical Micrococcus. Hence the number of 

 planes of division is not constant, and is therefore not a suitable 

 criterion for the classification of bacteria. 



(2) Motility. — In Migula's system a distinction is made 

 between a Sarcina and a Planosarcina, the former being non- 

 motile, and the latter motile. A similar distinction is drawn 

 between Micrococcus and Planococcus. Twenty-four species 

 of Sarcina, Micrococcus and Streptococcus were cultivated by 

 the author in such a way that the cells were as short a time 

 as possible in the presence of their excretions. The result 

 of such cultivation was invariably the same. The aggregated 

 cells were found to break up into uni-, diplo-, tri-, and tetra- 

 cocci, and at the same time motility was developed. Con- 

 versely, the aggregated stage was found to be a non-motile 

 one ; this loss of motility was correlated with an increased 

 slime-production. It was found possible by frequent sub- 

 culturing to reduce the slime formation and so to induce 

 motility in sixteen species of Sarcina, five species of Micro- 

 coccus, three species of Streptococcus, and five species of 

 Bacterium, all usually described as non-motile. The bacteria 

 investigated were the following : — ■ 



Sarcina piilmo)ium, auresce^is, flavescens, rosea, flava, mo- 

 hilis, fimentaria, gasoformans, striata, vermiformis , 

 oleus, ventriculi, fuscescens, marginata, and two 

 unidentified species. 



Micrococcus helvolus, citreiis, grossus, and two unidentified 

 species. 



Streptococcus tyrogenus, pallidus, and pyogenes. 



Bacterium hirtum, tomentosum, filamentosum, rugosum. 

 and cerinum (Ellis (i — 3)). 



