PHILIP HADLEY 99 



Of the influence of these various incitants, only a few brief statements may here 

 be made. First, dissociation cannot occur unless growth occurs; cultures in a state of 

 suspended growth, while still alive, remain fixed in the type in which growth last oc- 

 curred. This is not necessarily true of old cultures in which growth still takes place 

 slowly. This circumstance reminds us of the conditions limiting the action and re- 

 generation of the bacteriophage. Dissociation, moreover, occurs most freely in liquid 

 media, and most actively at a reaction point of pH 7,8-8,0. This, it may be noted, is also 

 the optimum reaction for bacterial autolysis in most species. In cultures frequently 

 transferred on favorable solid media, dissociation is more restricted and may even ap- 

 pear to be absent. When dissociation has occurred, and the R type has once been pro- 

 duced, this type of culture is more stable than the S, and much more stable than the 

 0, both on solid and in liquid media. The presence of phenol, pancreatin or lithium 

 chloride, and other chemical substances, favors the transformation of the S type to 

 the O type culture in some species. 



The influence of blood serum is of special interest. Sometimes a normal serum of cer- 

 tain species will force the reaction. This is likely to concern the serum of animals which 

 are not susceptible to the organism, or sera supposed to be germicidal. As mentioned 

 above, however, the strongest dissociation-furthering power is possessed by homologous 

 immune serum. This can be demonstrated by growing the S type culture for a few 

 generations in broth containing about 10 per cent of the immune serum, the result being 

 the formation of the R type culture. This has been demonstrated for the pneumococ- 

 cus, the streptococcus, B. subtilis, Friedlander's bacillus, B. typhosus, B. paratyphosus 

 B (SouleO, B, coli (Dulaney'), and some other forms. There is some evidence that 

 the same reaction occurs in vivo as well as in vitro; and this suggests the possibility 

 that the chief mechanism of protection of the bacteriotropic antibodies may repre- 

 sent merely the enforcement in the body of a dissociation of the invading organisms, 

 comparable to that observed in the culture tube. This possibility, which was first 

 approached by the researches of Griffith on the dissociation of the pneumococcus in 

 1923, 1 have considered at greater length in an earlier publication. With reference to 

 the effects of immune sera on the R and S culture types, it should be added here that 

 it has been shown for B. subtilis by Soule,^ for B. coli by Dulaney, for the pneumococ- 

 cus more recently by Avery, and for B. paratyphosus B by Soule, that, when the R 

 type culture is grown in serum immune to this culture form, a retransformation is 

 enforced to the original S, 



When one observes that the dissociative reaction can be precipitated by such di- 

 verse substances or conditions of growth as those mentioned above, the question of the 

 actual cause of dissociation seems to be as far removed as at the beginning. But the 

 situation may be simplified if we can discover a common factor among all of these in- 

 fluences. It seems safe to say that there exists such a common factor, and that it may 

 be defined as any condition or substance that is antagonistic to the continued growth 

 of the so-called "normal" culture type. That this factor may not be the same for all 

 bacterial species is a view that we may well accept, but that the same influence will 

 operate in the same manner on different members of the same group of bacteria seems 

 well demonstrated by numerous observations. 



' Personal communication, * Soule, M. S,: loc. cil. 



