272 S. ORLA- JENSEN 



Whereas the shape of cells was formerly used as a family 

 character, I have adopted it only as a generic one, and if we do 

 not want to further confine its signification and only consider it 

 as a specific character, we shall doubtless have to set up the 

 genus Propionicoccus besides the genus Propionihacterium. 



Microbacterium is to be understood as merely a provisional 

 collective name for Gram-positive rods of size a little smaller 

 than the ordinary bacteria. In biological respects some of these 

 rods {Bacillus acidophilus) are closely related to the true lactic 

 acid bacteria, whereas others approach the Tetracocci or the 

 aerobic bacilh. 



The genus Tetracoccus, including strictly aerobic as well as 

 strictly anaerobic-species, is probably of as polygenetic a nature 

 as is the genus Microhacteriu^n, and the genus Coccus perhaps 

 does not belong at all in the order of bacteria in question. In 

 biological respects the Gram-negative, strictly aerobic, chromo- 

 genic cocci certainly appear to attach themselves rather closely 

 to the genus Fluormonas; yet their place in the system cannot be 

 determined with certainty until the arrangement of the flagella 

 of the motile species has been studied. 



The genus Bacterium will undoubtedly dissolve into several 

 genera, of which I may especially mention the Colihacterium and 

 Aerogeneshacterium. The reason why I am now inclined, in 

 contrast to my earher opinion, to consider the coli- and aero- 

 genesbacteria as two different genera, is because they differ 

 not only in morphological, but, as later researches have shown, 

 also in biological respects. I have myself proved (1914), that 

 the Aerogenesbacteria completely oxidize the carbohydrates 

 when the nutrient matter offers a sufficient buffer effect, and 

 they thus correspond with their name in forming more gas than 

 do other bacteria, and Rogers, Clark and Davis (1914) have 

 shown that in the gas developed by the Colibacteria there is 

 proportionately more hydrogen than in that developed by the 

 Aerogenesbacteria. Perhaps the Committee is right in not 

 regarding the Proteus-bacteria (my genus Liquidomonas) as a 

 separate genus, as their whole metaboHsm indicates that they 

 are to be looked upon as gelatin-hquefying Coli- and Aero- 

 genesbacteria. 



