No. 615] 



BACTERIAL PHYLOGEXY 



243 



This nitrogen fixation must be carefully differentiated 

 from the nitrification previously discussed. Probably 

 the non-motile group Mycoderma which resembles the 

 other organisms in ability to oxidize sugars (preferably 

 ethyl alcohol), but is non-motile, should be placed here. 

 These three genera are obligate aerobes and secure their 

 growth energy by relatively complete oxidation of carbo- 

 hydrates, alcohol or even acetic acid. They apparently 

 constitute a natural group related to Pseudomonas. It 

 should be recalled that a statement of relationship does 

 not imply derivation, but simply common ancestry. 



We have now considered all the bacteria which show 

 the primitive characters of polar flagellation and obligate 

 aerobic utilization of carbonaceous foods. In the genus 

 Pseudomonas we find evidences of differentiation in me- 

 tabolism, particularly ability to bring about proteolysis. 

 In some species we have evidences of adaptation to 

 anaerobic conditions, among the so-called denitrifiers. 

 Some members of this group are capable of taking oxygen 

 from nitrite and nitrates under anaerobic conditions, with 

 evolution of free nitrogen. Other forms are known that 

 can reduce sulfates to sulfids. Such facultative an- 

 aerobes, securing oxygen from an easily reduced com- 

 pound, evidently make use of the oxygen in the same 

 manner as though growing under aerobic conditions for 

 the oxidation of carbon compounds. The next step in the 

 development of anaerobiosis was probably the utilization 

 of carbon compounds, securing growth energy by intra- 

 molecular oxidations; in such forms fermentative capacity 

 becomes well marked. 



The close relationship in morphology and physiology 

 existing between the short spiral Vibrio and Pseudo- 

 monas indicates that the family Spirillacece has come from 

 an ancestry having much in common with Pseudomonas. 



The other bacteria belonging to the\Eubacteriales are 

 more specialized in general morphology and in physiol- 

 ogy than the forms thus far mentioned, ^hen motiie the 

 cells are peritrichous rather than with pblar flagella. 



