NOMENCLATURE AND CLASSIFICATIONS. 175 



A very few of the preceding may perhaps some time make good their claim to 

 be considered as independent genera. Many of these names are preoccupied in this 

 group or in other groups ; some represent mixtures ; others, purely physiological 

 genera ; but some of them may be used within the limits of genera to designate 

 special physiological groups whenever such use leads to clearness of understanding. 



Naegeli, Beyerinck, and Winogradsky have studied especially the food require- 

 ments of bacteria. Many others have, of course, contributed. Alfred Fischer has 

 given a good summary in the second edition (p. 96) of his " Vorlesungen." Follow- 

 ing this, and considering them especially with reference to their nitrogen-nutrition, 

 the bacteria may be classified into seven groups : 



1 . Paratrophic bacteria. The obligate parasites, capable of growing only on substrata 



similar in composition to the fluids of the host. 



2. Peptone-bacteria. Organisms requiring peptones or albumoses. 



3. Amido-bacteria. Organisms which also grow well when their nitrogen food is 



restricted to amido-bodies asparagin, leucin, etc. but not able to use ammonia. 



4. Ammonia-bacteria. Able to take nitrogen from ammonia compounds. 



5. Nitrobacteria. The denitrifying organisms. They require organic carbon com- 



pounds. 



6. Nitrous and nitrate bacteria. The saltpeter-bacteria. Nitrates, nitrites, or ammo- 



nia-compounds furnish the necessary nitrogen. The carbon dioxide of the air 

 serves as their carbon-food. 



7. Nitrogen -bacteria. Organisms able to assimilate free nitrogen, but only in the 



presence of organic carbon compounds. 



In 1895 Wyatt Johnston suggested that all the important characteristics of a 

 species might be recorded by numbers arranged in a definite order. Gage & Phelps 

 and Kendall afterward made use of the Dewey numeral system. By this means 

 the leading features of a hundred or of five hundred organisms might be recorded 

 on a single page, so as to be very easily compared. Chester has modified this system 

 for application within the genus as follows: 



ioo. Endospores produced. 0.002 Acid without gas from saccharose. 



200. Endospores not produced. .003 No acid from saccharose. 



10. Aerobic and facultative anaerobic. .0001 Nitrates reduced. 



20. Anaerobic. .0002 Nitrates not reduced. 



1. Gelatin liquefied. .00001 Fluorescent. 



2. Gelatin not liquefied. .00002 Violet chromogens. 

 o.i Acid and gas from dextrose. .00003 Blue chromogens. 



.2 Acid without gas from dextrose. .00004 Green chromogens. 



.3 No acid from dextrose. .00005 Yellow chromogens. 



.01 Acid and gas from lactose. .00006 Orange chromogens. 



.02 Acid without gas from lactose. .00007 Red chromogens. 



.03 No acid from lactose. .00008 Brown chromogens. 



.001 Acid and gas from saccharose. .00000 Non-chromogenic. 



According to this scheme the formula for Bacillus coli and Bacterium campcutrc 

 would be respectively B. 212.11110 and Bact. 211.33315. Such a system admits of 

 indefinite extension, and the reader can see at a glance that, if well worked out so 

 as to include all the more important facts, it would be invaluable for unification of 

 methods and for quick, easy reference. Each group of digits should include as 



