PHILIP HADLEY 



97 



pendent activities. When removed and purified by plating methods, they afford new 

 forms of culture which sometimes manifest considerable permanence in their newly 

 acquired characters. It is these forms that have erroneously been regarded as mu- 

 tants. 



CHANGES IN CELL MORPHOLOGY 



Closely associated with the specific colony type, and in all probability determin- 

 ing, within limits, its characteristics, are to be observed some fairly distinct morpho- 

 logical characteristics of the cells and their organelles. Microscopic study of the type S 

 culture, which usually passes under the appellation of "normal culture," although ex- 

 ceptions have been noted, usually reveals a preponderance of those cell forms which 

 are regarded as characteristic of the "species" in question. The type R culture, on 

 the other hand, is likely to present a different picture; but this, in turn, varies with 

 the species. In the members of the intestinal group the well-stabilized R type cell is 

 most often coccoid, and a similar shortening is characteristic of the R forms of the 

 diphtheria bacillus, the plague bacillus, probably of the tubercle bacillus and of several 

 other species. In other cases, as in B. subtilis, B. anthracis, and perhaps in all the spore- 

 formers (none of which, with the exceptions noted, has been carefully studied), the 

 R type are much more elongated than the S type cells and are sometimes distinctly 

 filamentous. 



The nature of the cell population of the O t^-pe cultures is not so clearly recog- 

 nized. But it may be affirmed that, in comparison with the S and R, it is highly di- 

 verse. It is particularly in cultures of the O type that one finds amassed those peculiar 

 cell bodies which, for many years, have been termed "involution forms." They con- 

 tain long, swollen rods, filaments (often fungoid in nature), giant coccoid bodies, 

 apparently identical with Kuhn's Pettenkofer bodies, zygospore-like bodies, and often 

 numerous minute granules, the exact nature of which is perhaps still in doubt, although 

 it seems probable that some of them arise from the zygospores. The whole picture is 

 extremely bizarre but is fairly constant for the intermediate type cultures of many 

 bacterial species. Such forms have been produced by Kuhn and others by growth on 

 media containing traces of lithium chloride. But it is sufficient to convince us that, 

 under the cover of these bacterial monstrosities, are proceeding reproductive events of 

 which we have, as yet, slight cognizance. Of one point, however, we may be assured. 

 These peculiar forms are not "pathological" nor evidences of degeneration. They have 

 been termed "involution forms"; but, as Mellon has suggested, "evolution forms" 

 would be more appropriate. The details of their production and reproductive be- 

 havior constitute at present one of the most important problems in microbic dissocia- 

 tion. It seems possible that in their action is hidden the problem of the filtrable forms 

 of bacteria, if not of the filtrable viruses; also perhaps the mystery of the bacterio- 

 phage. 



Just as the morphology of the bacterial cell is correlated with the type of culture, 

 so also are correlated motility, capsule formation, and perhaps spore formation. The 

 time is past when we can state with discretion that such and such a bacterial "species" 

 is motile, for both motility and flagellar equipment depend on the cyclostage. Up to 

 the present time, observations seem to indicate that, if an organism shows motility, 

 it belongs to the S type as opposed to the O or R, which are commonly non-motile. Ark- 



