448 R. S. BREED, H. J. CONN AND J. C. BAKER 



tioned represent the lines of development of the bacteria more 

 truly than the physiological groups proposed by Jensen. 



It is next necessary to take up in turn the seven families into 

 which the committee has divided the order Eubacteriales. 



Family 1. Nitrobacteriaceae. The justification for the recog- 

 nition of this family is given in the following quotation from the 

 committee report (p. 542) : 



The Nitrobacteriaceae are clearly the most primitive of the Eu- 

 bacteriales. Their power to live without complex organic substances 

 would have made it possible, as Jensen points out, for them to flourish 

 at a very early period in the world's history, and their simple struc- 

 ture is in harmony with the view that they represent the ancestral 

 type of all other bacteria. 



To accept this family, then, is really to endorse the theory that 

 its members are modern representatives of the primordial 

 bacteria. 



Before endorsing that theory, however, it seems well to con- 

 sider what evidence we have concerning the primordial types of 

 bacteria. Such evidence cannot be obtained by paleontology, 

 as when higher forms of life are concerned. What evidence 

 we have from fossils as to the existence of bacteria in past ages, 

 although scanty, is very interesting.^ Recent deductions, how- 

 ever, such as those of Kligler (1917, p. 166) and of Osborn (1916, 

 p. 292, and 1917, p. 86), as to the kinds of bacteria living in these 

 early days, based upon the supposed protoplasmic structure of 

 these fossilized organisms, will hardly be accepted by conserva- 

 tive bacteriologists. 



Jensen's speculations as to the earliest forms of life are based 

 upon chemical and physical considerations rather than upon 

 paleontology and perhaps have a firmer foundation than those 

 which rest upon Walcott's observations. Jensen concludes 

 that the autotrophic bacteria were the first organisms on the 

 earth, because they are the only known forms of life which can 

 live upon inorganic matter without the action of sunlight, and 



^ See Walcott's evidence (1915) as to bacteria in Algonkian limestone-, and 

 Moodie's discussion (1916) of their existence in Mesozoic times. 



