ROGER G. PERKINS 131 



and its associates with diphtheria and its associates and to consider them both as re- 

 lated to the thread fungi which have true branching. It is also the prevailing practice 

 where Nocardia is used to confine this to the special group noted above. It is to be 

 hoped that a better agreement may develop in this group. 



Spiral fonns. — There has naturally been much contest as to the placing of these. 

 One school places all spiral forms, from the cholera organism to the treponema and 

 its associates, in one group, subdivided into: (c) simpler forms long known to us 

 as the cholera group; and {b) the more "protozoan-like" (if that means anything), 

 including treponema, leptospira, spirochaeta, etc. Another school places this second 

 group in a completely separate division, leaving the others in Spirillaceae {q.v. infra). 

 Some believe the "protozoan-like" group to be intermediate between bacteria and 

 protozoa but it is interesting to find recent textbooks on protozoa omitting it entirely 

 (Hegner and Taliaferro, Craig). (See Table I for details). In general, the first of the 

 two groups corresponds to Spirillaceae Migula (1894) emended Committee, So- 

 ciety American Bacteriologists (1917), with the following description: "Cells elon- 

 gate, more or less spirally curved. Cell division always transverse, never longitudinal. 

 Cells non-flexuous. Usually without endospores. As a rule motile by means of polar 

 flagella, sometimes non-motile. Typically water forms, though some species are in- 

 testinal parasites." The second corresponds in the same way with Spirochaetaceae 

 (Swellengrebel) described by the Committee as follows: "Free living or parasitic 

 spirilliform organisms with or without flagella, with undulating or rigid spiral twists. 

 Reproduction by transverse division and by 'coccoid bodies,' the equivalent of 

 spores." 



This brings us to the group of true bacteria (Eubaderiales , Buchanan) (see 

 Table I). 



This vast group of simplified forms, aerobic and anaerobic, spherical and rod 

 shaped, pigment formers or non-pigment formers, fermenters or non-fermenters, mo- 

 tile or non-motile, gram positive or negative, spore-formers or non-spore-formers, and 

 with many other positive and negative characters, has been divided and subdivided 

 on the basis of combinations of these until there is practically no theory which may 

 not find substantiation in published work. The minimum number of divisions under 

 this head is three: the spherical forms, the rod forms, and the spiral forms. 



Spherical forms. — This group was recorded as Coccaceae by Zopf in 1884 and is 

 the most widely accepted of all, including all spherical forms of whatever arrange- 

 ment, with certain minor and not undisputed exceptions. 



In spite of possibilities that in the development of bacteria there may be a ten- 

 dency for cocci, especially when there are one or more flagella, to elongate, it seems 

 agreed by most observers that the spherical forms are worthy of a grouping of their 

 own, and the rod forms likewise. If one selects habitat, or fermentation, or color, or 

 motility, or pathogenicity as prime factors, this grouping will at once disappear. Some 

 observers (Orla- Jensen) believe that the chain-cocci and the chain-rods are to be con- 

 sidered together, but their arguments, though interesting, are necessarily based on 

 theoretical grounds, and, as noted elsewhere, our actual, objective knowledge of the 

 evolution of bacteria from the original, whatever it was, is mostly speculative. 

 Whether the modern work on variation will reach a point from which we may argue 



