ROGER G. PERKINS 127 



will be seen later, even the arguments for early historical precedence are not generally 

 accepted. In other words, are not most of these chemical and physiological characters 

 even less definite and stable than morphology, and should not their use begin where 

 the criteria of morphology alone are inadequate? It has, of course, been frequently 

 brought out that characters important in one group are unimportant in another, as, 

 for instance, fermentations in the cocci and in the bacilli, or character of division in 

 the same groups. It is probably impossible to formulate as a rule whether a given 

 character should always define species or confine itself to varieties. 



HABITAT AS A DIFFERENTIAL POINT: PATHOGENICITY 



"Pathogenicity may be taken as a type of those powers of the organism which are 

 easily and profoundly modified by external conditions." This quotation from Wins- 

 low in 1906 seems incontestable, yet later he uses "habitat" in the separation of his 

 genera in the Coccaceae. This seems rather inconsistent even though he insists upon 

 groups of characters rather than individual ones. Here, again, there is marked dis- 

 agreement, as Hucker differs from Winslow in a similar paper, as follows: 



Due to the fact that the micrococci are found in such a wide variety of sources, and due 

 to their ability of adaptation to various environments, the use of habitat alone as a char- 

 acter in separating the general group is precluded. It is true also that no other character will 

 definitely correlate with the source of the different types and bear out any conclusions that 

 different natural groups of micrococci can be secured from different habitats. 



It would seem that if this applies to this group, other groups in which the same ob- 

 jections hold true would be similarly affected. 



It has always seemed to me that the selection of pathogenicity as a prime factor 

 of division is only part of the pride of the human race in its superiority, a pride which 

 has from time to time admitted some of the lower animals under the wider cloak of 

 animate, moving life. In the consideration of bacteria, however, why should one 

 metabolic activity be superior to another? We believe that pathogenicity is more or 

 less of an accident, that bacteria are not toxic in order to be pathogenic, but pathogenic 

 because they happen to be toxic. Because some by-product of digestion when applied 

 to a mucous membrane causes death and breaking down of the local cells, whereas 

 other products of digestion can break them down only after cell death, may be a 

 matter of degree rather than character. Non-bacterial poisons may have the same 

 effect, but are not classified on this basis, but rather on the general character of their 

 possible chemical combinations. Should we not therefore consider the chemical activ- 

 ities of bacteria, due to metabolic products with various chemical characters, rather 

 on the basis of these characters alone than on some special reaction, which is, as Wins- 

 low (1905) calls to our attention, readily modifiable by environment? Breed, Conn, 

 and Baker {loc. cit.) criticize the Society of American Bacteriologists' Committee 

 (1917) in that "too great weight has been placed on pathogenicity," attacking special- 

 ly Hemophilus, Pasteurella, and Erwinia. It seems to me dangerous in a general clas- 

 sification to say that a group is generally, or usually, or essentially parasitic, in view 

 of the well-known fact, already recalled, that our knowledge of bacteria is confined 

 to a very small fraction of the total in existence, and since scarcely any groups which 

 contain pathogens do not include forms closely related but without pathogenicity. 



