March 29, 1918] 



SCIENCE 



323 



If descriptions of such organisms are non- 

 axistent in the literature is it necessary to 

 assume that they have not been discovered or 

 that they once existed but have disappeared? 

 Is it so evident that 



The line of descent from the prototrophic deni- 

 trifiers is entirely clear. 



The statement is made that next in series 

 following the prototrophic denitrifiers prob- 

 ably came the aerogenes type of organism, one 

 indication of relationship being that it can 

 live " in simple inorganic media and under 

 certain conditions, even to fix atmospheric ni- 

 trogen." The present writer has been unable 

 to find any evidence that the aerogenes group 

 can ever grow in a medium devoid of organic 

 matter. It is true that inorganic nitrogen 

 compounds may be used, but this, as was above 

 indicated, has no particular significance, as 

 many bacteria, yeasts, molds, algae and even 

 flowering plants have the same power. Any 

 close relationship of aerogenes to a proto- 

 trophic form certainly has not been proved. 

 However, the author's claim for close rela- 

 tionship between aerogenes and coli and 

 through the series to the typhoid, dysentery 

 and possibly even to the hemorrhagic septi- 

 cemia groups has much to commend it, and is 

 a generally accepted hypothesis at present 

 among bacteriologists. 



It is possible that the relationship assumed 

 to exist between B. proteus and the spore- 

 bearing rods is a real one, but the structural 

 modification incident to the development of 

 the power of endospore production is so great 

 that mere association of organisms in putre- 

 factive processes and common property of pro- 

 ducing proteolsrtic enzymes does not prove 

 close affinity. It should be home constantly 

 in mind that proteolytic enzymes are com- 

 monly produced by cells. Every cell has pro- 

 toplasm consisting largely of protein. Cells 

 in general after death undergo autolysis. 

 Every cell then contains an autolytic pro- 

 teolytic enzyme. The step to the production 

 of an extracellular proteolytic enzyme would 

 therefore seem not to be a difficult one to 

 make, and one which may have been made 

 independently by different groups. It might 

 be mentioned, however, that Kligler has ig- 



nored one point of morphology which would 

 tend to show relationship better than proteol- 

 ysis, this being the diffuse arrangement of 

 the flagella in both groups. Apparently or- 

 ganisms showing peritrichous flagella consti- 

 tute a group rather distinct from the forms 

 with polar flagella. 



The type of pigment produced, and the gen- 

 eral cultural and physiological characters 

 would seem to argue quite as close a relation- 

 ship between the Rhodococcus and Micrococcus 

 and the rods producing red or yellow pigment, 

 as between the latter and the spore-bearera or 

 B. proteus. Many more resemblances than 

 differences will be found, for example, between 

 Rhodococcus roseus and the organism usually 

 known as Bacillus prodigiosus. 



The effort to derive the gram positive strep- 

 tococci from the aerogenes types seems rather 

 strained. Differences are more marked than 

 resemblances. The products of fermentation 

 are very distinct in the two groups. This fact 

 together with decided differences in morphol- 

 ogy, relationship to oxygen and cultural char- 

 acters, counterbalance the presence of capsules 

 of similar composition, ability to ferment 

 inulin (in fact a variable character in aero- 

 genes) and localization in the same organs of 

 the animal body. However, it should be 

 granted that the author's emphasis on rela- 

 tionship between the streptococci and the 

 aciduric bacilli is probably well placed. 



Kligler's characterization of Azotobacter as 

 a form not only fixing atmospheric nitrogen 

 but oxidizing nitrogen to nitrates is apparently 

 not well founded. It may be noted that there 

 is an apparent tendency to consider Azoto- 

 bacter prototrophic, an assumption which is 

 quite unwarranted. The statement " the Azo- 

 tobacter can assimilate free nitrogen more 

 readily if glucose and a small amount of am- 

 monia are supplied" is misleading. Appar- 

 ently Azotobacter is wholly incapable of grow- 

 ing, certainly incapable of fixing atmospheric 

 nitrogen, without an abundance of soluble 

 carbohydrate food. By oxidation of this car- 

 bohydrate, energy is secured for the fixation 

 of sufficient atmospheric nitrogen for the 

 needs of the cell, but there is apparently no 

 nitrogen changed into the form of nitrates. 



