40 BIOLOGY AND TECHNIQUE 



venience than of actual scientific classification. Thus, for instance, 

 all stages of metabolic activity fill in the gap between the synthetiz- 

 ing sulphur and nitrifying bacteria and the purely katabolic activ- 

 ities 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 condi- 

 tions are subject to the widest variations, from those of an indis- 

 putably useful saprophytism to those of the most exquisite para- 

 sitism. 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 convenience clas- 

 sified 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 



I 



ALGJE LICHENS FUNGI 



| 



SCHIZOMYCETES BLASTOMYCETES HYPHOMYCETES 



(Bacteria) (Yeasts) (Molds Oidia) 



I 



Coccacea Chlamydobacteria 



Bacteriaceae (Higher bacteria) 



Spirillaceae Streptothrix 



Cladothrix 

 Leptothrix 

 Actinomyces 



The special classification of the bacteria has offered still greater 

 difficulties, for the lower we proceed in the phylo genetic scale of 

 living beings, the less specialized the morphological and biological 

 characteristics of any group become, and the more difficult it is to 

 establish a classification which can in any way be regarded as final. 

 It is, therefore, quite impossible to classify the bacterial varieties or 

 species on any basis which can hope to satisfy all the demands of 

 scientific accuracy and it is necessary to resort to the expedient of 

 utilizing some one characteristic which remains constant for the 

 individual genus and to base upon this an attempt at grouping. 

 When bacteria were first discovered, and for many years following, 

 numerous observers contended that the form of the microorganism 



