RELATION TO ENVIRONMENT CLASSIFICATION 35 



THE CLASSIFICATION OF BACTERIA 



Too simple in structure, too varied in biological properties to be 

 definitely identified with either the vegetable or animal kingdom, the 

 bacteria are placed at the bottom of the scale of all living beings. Closely 

 linked on the one hand to the plant kingdom by the yeasts and the 

 molds, and on the other to the animal kingdom by the protozoa, they 

 themselves combine, within one and the same division, attributes so 

 widely divergent as to structure, metabolism, and biological activity that 

 their grouping is more a matter of working convenience than of actual 

 scientific classification. Thus, for instance, all stages of metabolic ac- 

 tivity fill in the gap between the synthetizing sulphur and nitrifying 

 bacteria and the purely katabolic activities of some of the aerobic and 

 anaerobic microorganisms which cause putrefaction. Growth takes 

 place within the limits of a wide temperature range, and the specific 

 modes of life and cultural conditions are subject to the widest varia- 

 tions, from those of an indisputably useful saprophytism to those of the 

 most exquisite parasitism. Although, therefore, strictly speaking, the 

 bacteria can be classified as a whole neither in the animal nor in the 

 vegetable realms, being nonchlorophyll-bearing, they are for conve- 

 nience classified with the fungi or colorless plants. 



The relationship of the bacteria to other simple plants may be 

 graphically represented by the following scheme: 



CRYPTOGAMIA. 



! 



THALLOPHYTA. 



ALG^E. LICHENS. FUNGI. 



SCHIZOMYCETES BLASTOMYCETES HYPHOMYCETES 



(Bacteria). (Yeasts). (Moulds Oidia). 



Coccacea. Chlamydobacteria. 



Bacteriacese. (Higher bacteria.) x 



Spirillaceae. Streptothrix. 



Cladothrix. 

 Leptothrix. 

 Actinomyces. 



The special classification of the bacteria has offered still greater 

 difficulties, for the lower we proceed in the phylogenetic scale of living 

 beings, the less specialized the morphological and biological charac- 

 teristics of any group become, and the more difficult it is to establish a 



