126 CLASSIFICATION OF BACTERIA 



I must confess, however, that on tabulating the one group against the other, save for 

 the fact that more of the peritricheae are pathogenic, the evidence of superiority ap- 

 pears inconclusive. It does not seem to me that our knowledge of bio-chemistry is 

 sufficient to show that the power to utilize or break down certain chemical compounds 

 proves more or less "advancement," and the analogies with the protozoa, while un- 

 questionably fascinating, seem to me to stop at that point. 



Without plunging too deeply into controversy, one may say that the division on 

 the basis of spore formation is logical, as showing a major activity, and is widely ac- 

 cepted, though the resultant group is variously placed. Some (Table I) accept this 

 character as a basis for families under the Euhacteriales , others prefer tribal divisions 

 under the family of rod forms, others as divisions of even lower rank. Classifications 

 such as Orla-Jensen's (1921), fundamentally based on physiology and chemistry, are 

 much less interested in spore formation. 



How far should the differentiation by morphology carry? It seems to me that 

 this basis can certainly carry us as far as genus, and Hall (1927) goes further, saying: 

 'T submit that morphologic criteria should enable us to identify the genus, and I be- 

 lieve that the definition of orders, families and genera should be based solely upon 

 morphologic data." With this sentiment many but by no means all agree. 



CHEMISTRY AND PHYSIOLOGY 



The most extensive changes have been due to attempts to use the activities of the 

 bacteria rather than their form and arrangement as differentiating factors. The 

 changes have ranged from a practically complete substitution, such as Orla-Jensen's 

 (after the original flagellar division), to studies of small fractions of the problem. The 

 general tendency of taxonomists is to emphasize morphology in the larger groupings 

 and to reserve biological activities for smaller collections. Pigment formation, prob- 

 ably the earliest observed of the definite chemical activities, has been graded all the 

 way from family to variety, sometimes in connection with other group characters, 

 sometimes practically alone. No very adequate reason has been adduced why groups 

 of chromogenic organisms with different metabolic activities should be classed by 

 their pigments rather than distributed according to their other characteristics. It is 

 true that we have a very moderately studied collection of pigment-formers with little 

 else by which to classify them and that this procedure may be temporarily convenient. 

 But why the power to use fixed oxygen rather than free oxygen, or to break down sug- 

 ars, or to form complex toxins or proteolytic ferments is not as remarkable as the 

 power to form pigments, has never been demonstrated to my satisfaction. Hucker {loc. 

 cit.) states in regard to the cocci: 



It seems evident that pigment production by the mass-forming cocci is a very important 

 character for use in classification. However, due to its general lack of correlation with other 

 characters, it does not appear that the group should be divided into genera with differences 

 in chromogenesis as the chief diagnostic feature. On the other hand it seems that pigment 

 production is sufficiently constant to warrant its use as a character of importance in differ- 

 entiating species, and when so used should be interpreted along broad lines rather than to 

 attempt to make fine distinctions in shades of color. 



In the same way the "nitro-" bacteria, placed as high as a family by some, a sub- 

 family or tribe by others, seem to be getting more attention than they deserve. As 



