loo DISSOCIATIVE ASPECTS OF BACTERIAL BEHAVIOR 



Regarding the permanence of the dissociates, with their newly acquired char- 

 acters — it has of ten been stated that they are irreversible; and, for this reason, they 

 have often been described in the literature as mutations. This interpretation has con- 

 cerned the O forms much less often than the R, for the former are notably unstable. 

 Even the R types represent a series in which the degree of stability is very variable. 

 It seems to depend, in part, upon the length of time that the R culture has been prop- 

 agated continuously under the conditions that gave rise to it. The longer the stimulus 

 is applied, the more stable the type seems to become. There are, however, some ex- 

 ceptions to this. Some R type pneumococcus cultures are apparently irreversible; and 

 the same is true of some R type Friedlander strains, according to Julianelle.' The R 

 form of B. paratyphosus, B. typhosus, B. sicipestifer, B. dysenteriae, Bad. lepisepticum, 

 B. diphtheriae, B. subtilis, and B. anthracis have been found highly stable, and have 

 sometimes been reported as permanent variations. But Jordan,^ by a special method 

 of cultivation, succeeded in causing the reversion of his R type of B. paratyphosus B; 

 end Soule, by growth of his R type of B. subtilis in an R immune serum, was finally 

 able to cause a return to the S type of culture. Later he was able to cause the reversion 

 of an R type of B. paratyphosus B by similar measures. Mellon^ has emphasized the 

 stabihty of variants of his diphtheroid forms, and I have been unable to effect the 

 retransformation of an R type of B. pyocyaneus even after four years, although I have 

 not tried the action of R immune serum. Apparently, the R forms of culture may 

 remain stable for many years, but I believe there is no justification for the conclusion 

 that they represent hereditary variations or mutations in the strict meaning of the 

 term. It is more likely to mean that we have not yet been able to discover the 

 adequate means for causing their return to the original form of culture. 



BIOLOGICAL SIGNIFICANCE OF DISSOCIATION 



In concluding this chapter the question arises. What is the deeper meaning of these 

 phenomena concerned with the separation of bacterial cultures into distinct compo- 

 nents whose nature and behavior we have now briefly reviewed? It can mean only 

 one thing: that those living cells that we have commonly regarded in past years as 

 among the simplest of plant forms, and characterized by a correspondingly simple re- 

 productive apparatus, possess in reality a highly complex genetic mechanism, which 

 enables them to reveal, in cultures, pictures of morphological and physiological di- 

 versity with which our old and limited notions of "reproduction by simple fission" are 

 utterly unable to deal. Although we may not yet be justified in accepting Enderlein's 

 view of actual sexual reproduction among the bacteria, we must accept the fact that 

 the nuclear equipment and reproductive behavior of bacteria are highly complicated 

 matters. We can no longer doubt that the hereditary mechanism in bacterial cells 

 makes provision for amphimixis, so long denied to these forms; nor can we hesitate in 

 accepting phenomena of gonidia formation, zygospore formation, and perhaps a kind 

 of budding, as common methods of bacterial reproduction. In all of these matters 

 bacteriologists as a class have combined in denying the existence of things that they 

 have not been willing to take the trouble to search for. 



' Julianclle, L. A. : loc. cit. 



^ Sec Hadley, Philip: loc. cit. ^ Mellon, R. R.: /. Med. Rcscirch, 42, 6i. 1920. 



