PHILIP HADLEY 95 



B. aerogenes. They often manifest a mucoid consistency. Cultures of this sort commonly ap- 

 pear in members of the colon-typhoid-dysentery group; also in B. anthracis, S.fecalis, and 

 probably other species. In B. anthracis some of these colonies are slimy and readily coalesce 

 on the agar plate. Similar colonies have been reported for various species among cultures 

 resistant to the bacteriophage. In B. proteus the equivalent oMhe S form yields a spreading 

 growth while the growth of the O type is restricted. In several species, such as pneumococ- 

 cus, streptococcus, meningococcus, and gonococcus, the O type has not been described 

 clearly. In general, it is highly unstable and may sometimes transform with great rapidity 

 into the R. Such cultures have been termed "suicide cultures." They are very difficult to 

 maintain on agar, and it is sometimes impossible to cultivate them in broth. It is reason- 

 able to believe that the O colony form is at some time present in cultures of all bacterial 

 species, but may pass unobserved. Certain members of the intermediates, such as those 

 representing the Pettenkofer bodies of Kuhn, may play an important role in the phenom- 

 enon of the bacteriophage, as I have pointed out elsewhere.' 



Although it often appears that the three chief colony types (S, O, and R), but particu- 

 larly S and R, are clear cut in their essential features, and usually quite stable on appropriate 

 medium, in other cases there may be observed distinct intergradations; and these may take 

 on various aspects. For example, the S type colony may show, about its edge, either at a 

 single point or about its entire circumference, an outcropping of the R type culture. Inter- 

 esting examples of this have been described by Soule for B. subtilis, and observed by Nun- 

 gester for B. anthracis; also by Faith Hadley for S. Jecalis.^ The fairly smooth and circum- 

 scribed S colony, possessing (subtilis) the shallow fringe of filaments extending outward from 

 the border ("bayonet-front" effect), sends out longer outgrowths which soon begin to curl 

 under and to give a marginal appearance which simulates that of the R type anthrax colony 

 (Soule). This outgrowth is bluish and translucent by transmitted light and rough by re- 

 flected light. The result of this reaction is to yield an S type colony imprisoned within a ring 

 of R type culture, the breadth of which varies with conditions which cannot be considered 

 here. The type S anthrax colony may undergo transformations similar to those mentioned 

 above (Nungester). Such outgrowths have been termed the "halo" or "regeneration fringe." 

 In some cases, as in B. proteus for example, the halo may be made up of O type rather than 

 S type culture. Indeed, there may be a series of alternate dissociations and recoveries, fol- 

 lowing each other at intervals of a few hours, in the growth of the colony, the final effect 

 being the production of the typical "ring growth" characteristic of B. proteus. 



But the O type colony also may send out such regeneration fringes; and in this case the 

 nature of the fringe growth seems to depend on the degree of stability of the O colony. If it 

 is in the early intermediate state, it usually forms a halo of normal S culture. If it is in the 

 late intermediate state, it is more likely to send out a fringe of R type culture. Under these 

 conditions, culturing from the center or from the edge of the colony will yield cultures of two 

 different forms. The natural destiny of the type O culture is apparently to attain the R; and 

 it usually accomplishes this in the course of time. It is often difficult to maintain the inter- 

 mediate form in this culture state. The O form of B. proteus seems to be unusually stable, but 

 here the R form has not been recognized with certainty. It may be added here that it has 

 not been observed clearly that the type R culture gives regeneration fringes. It may, how- 

 ever, as we shall see later, produce clusters of S type secondary colonies which usually appear 

 on the free edges of growth; and these are analogous to the fringe, since it can be observed 

 that it is by the coalescence of numerous colonies appearing at the margin of growth that the 

 distinct fringes are produced. 



' See Hadley, Philip: loc. cit. Also Arch, of Path, and Lab. Med., 1928. In press. 



^ Personal communication. 



