94 DISSOCIATIVE ASPECTS OF BACTERIAL BEHAVIOR 



of the pneumococcus (Griffith,' Reimann,^ Amoss^), of B. diphtheriae (Corbett and 

 Phillips),^ of Sp. finkler-prior (Firtsch)," and of V. cholerae (Eisenberg,^ BalteanuO 

 differ from one another to such a degree that, on morphological grounds, all of the 

 variants would be regarded as contaminations — indeed, often have been so regarded 

 and treated accordingly. As one illustration of this, and as Soule^has already pointed 

 out, it may be noted that the R type colony of B. subtilis on plates is almost indistin- 

 guishable from the R type colony (Medusa-head type) of B. anthracis. On the other 

 hand, one may conclude from the studies of Nungester^ that the S type anthrax 

 colony is one that few investigators have ever seen, or at least recognized; and one 

 which would commonly be taken as a contamination, so different is it from the common 

 Medusa-head type. It is thus a rather curious fact that, while it is the S colony form 

 of B. subtilis that has come to be regarded by bacteriologists as the "normal," it is 

 the R type colony of B. anthracis which, during the fifty years of study that this 

 species has received, has become established as the "normal" form of culture. 



In most bacterial species for which knowledge is available, the colony of the S type is 

 smaller and more delicate than the other forms. It is round, even, usually opaque (even when 

 young), and, in certain species such as those of the intestinal group, the streptococcus, the 

 pneumococcus, the proteus, the pneumobacillus, and others, presents a glistening luster or 

 "moist" appearance. In addition, a distinct fluorescent effect by transmitted light is usually 

 seen (intestinal group, pneumobacillus, proteus, and others). The co'ony consistency is 

 commonly soft or butyrous. Such colonies, after four or five days' growth on rich and some- 

 what alkaline agar, often show pale or translucent, wedge-shaped invaginations where disso- 

 ciation into the O or R types is under way. Culturing from these "blue" areas will give cul- 

 tures of a quite different type from the original, but usually not well stabilized at this stage. 

 Repeated culturing, accompanied by colony selection, will increase the stability of the (com- 

 monly obtained) R form. 



The R type colony presents, in most species, a quite different appearance from the S 

 form. It is usually larger, irregular in shape, uneven; when young it is thin and translucent, 

 and reveals a distinctly rough surface, or sometimes merely a dull luster as in B. subtilis 

 (Soule). The fluorescent effect is invariably lacking. Old colonies, however, may become as 

 opaque as those of the S form. The consistency of the R colonies is sometimes similar to that 

 of the S form, but often, and when they are well stabilized (as in the "extreme" R), they may 

 be hard or even brittle, so that they may be pushed about over the agar surface. These have 

 been observed in the pneumococcus (Griffith) and in the streptococcus (Cowan). One curious 

 feature of the R type colonies of several species (B. diphtheriae, B. mallei, B. proteus, V. 

 cholerae, V. proteus, B. mesentericus, meningococcus, 5. fecalis, and probably other species) 

 is that they may take on a yellow or brown chromogenesis. Apparently a similar phenom- 

 enon occurs in the fungus of blastomycosis (Mellon).* I have also observed brownish colo- 

 nies arising in the dissociation of M. citrcus. 



Regarding the colonial features of the type O cultures, first clearly pictured by Firtsch 

 in 1888 for V. proteus, we have less knowledge. In general, the O colonies are larger than the 

 S, round, even, smooth, glistening, but more fleshy and convex, simulating the colonies of 



' Griffith, F.: loc. cit. 



2 See Hadley, Philip: loc. cit. «> Soule, M. S.: loc. cit. 



3 Corbett, L., and Phillips, G.: /. Path. &' Bad., 4, 193. 1897. 



-• Firtsch, G.: loc. cit. ' Nungester, W.: loc. cit. 



5 Balteanu, I.: loc. cit. * See Hadley, Philip: loc. cit. 



