128 CLASSIFICATION OF BACTERIA 



Can we determine habitat by a limited series of findings? Any organism that requires 

 oxygen, moisture, warmth, and broken-down organic matter may develop on the 

 surface of the body and remain there for various periods of time. It will also survive 

 or develop anywhere else under similar conditions, but would not be called parasitic 

 if found on a filthy blanket, 



HABITAT OTHER THAN PATHOGENIC 



The same general criticisms are applicable. It is unquestionably valuable to know 

 that most of a group have been isolated from water or soil or mucous membranes, 

 but the connotation to the average reader is that there is some inherent relation be- 

 tween the organisms and the particular environment. And this may or may not be 

 the case. This is a dififerent question from that of taxonomic names, and whether such 

 a definition is misleading or not is a matter of sharp controversy. 



CHRONOLOGICAL CLASSIFICATIONS 



Orla-Jensen (Joe. cit.) and Kligler (1913) have presented more or less elaborate 

 classifications on this basis, and a large part of the former's grouping, especially that 

 relating to the nitro-bacteria, has been taken over by the Committee of the Society 

 of American Bacteriologists. Breed, Conn, and Baker {loc. cit.) make a well-consid- 

 ered attack on both these systems, emphasizing that we are now dealing with end- 

 processes of evolution and not the primary forms except in so far as environmental 

 conditions have remained more or less permanent. (It is likely that conditions even 

 in water are not now identical with those of the period of origin of bacteria.) They quote 

 the Committee in their definition of the Nitro-bacteriaceae, and state that if we ac- 

 cept this family, we indorse the theory that its members are modern representatives 

 of the primordial bacteria. They object to this, and indicate that the theory, while 

 interesting, is without adequate proof. (Buchanan [1918] attacks Kligler's paper even 

 more sharply.) The most logical reason adduced for family rank is the close relation 

 of rods and spheres in this group and the inconvenience of separation. 



It seems to me also that in this question of primordial relations as a basis for di- 

 vision, too little notice has been taken of the well-recognized fact that characters may 

 be lost as well as acquired. An organism once able to utilize and synthesize simple ma- 

 terials may, under conditions of parasitism or even symbiosis, lose those powers, and 

 in the vast numbers of generations of bacteria it is not far fetched to consider the 

 possibility that strains with certain powers may lose part of them under changed en- 

 vironment, and under subsecjuent changes may either regain what was lost, acquire 

 new powers, or any combination of these two changes. Orla-Jensen shows that it is 

 quite probable that actual changes in form from sphere to rod may have taken place, 

 and botanical and zoological alterations due to environment under short-time ex- 

 perimental conditions are well known. Conclusions drawn from the conditions of 

 light, heat, available food, etc., in those geological periods during which bacteria de- 

 veloped are based on disputable evidence, and must be considered cautiously. 



IMMUNOLOGY 



This division of scientific work is still in its infancy, and its application to classifi- 

 cation of bacteria has been unsuccessful, save in the differentiation of varieties, and 



