THE FORMATION OF CELL-AGGREGATES 35 



In regard to bacteria in general, there is clearly no justification for ignoring such 

 observations as those recorded above ; but the thesis, that the bacterial forms 

 with which we are most famiUar in artificial cultures are only stages in some more 

 complex cycle of development, has not in our view been clearly and definitely 

 established. All bacteriologists are familiar with the so-called " involution forms " 

 to which we have already referred ; and there is little doubt that many of these 

 forms represent dead or dying cells. It may well be that we have been too ready 

 to refer to this category every abnormal form encountered ; and few would deny 

 that some of the appearances that are met with are strongly suggestive of some 

 more complex form than the simple bacillus. The problem is, however, beset 

 with technical difficulties arising from the small size of the organisms concerned. 

 The crucial test must remain the actual observation of the reproduction of typical 

 bacterial cells from the granules, spheres, or syncytial masses which have been 

 described as stages in the complete life-cycle ; and the unequivocal demonstration 

 of this cyclical development demands the isolation of single cells, not only at the 

 commencement of the cycle, but at each successive stage. No harm will be done 

 by maintaining a severely critical attitude at the present stage of the controversy, 

 so long as each new piece of evidence is considered on its merits. 



In this connection, the work of Klieneberger and of Dienes may be noted. Khene- 

 berger (1935) describes a minute pleuropneumonia-like organism in symbiosis with Strepto- 

 baciUus moniliformis, and considers that many of the morphological peculiarities that 

 are commonly regarded as characteristic of the bacillus are, in reality, due to the presence 

 of the symbiont. She suggests that some, at least, of the pleomorphic elements in bacterial 

 cultures that have been described as belonging to a sexual or developmental cycle may 

 have a similar origin. This view has been developed in subsequent publications (see 

 Chapter 40). Dienes (1942), on the other hand, believes that the pleuropneumonia-like 

 organisms are part of a life cycle not only in the streptobacillus, but in other bacterial 

 species. He has succeeded in inducing their appearance in cultures of Bad. coli, Hcemo- 

 philus influenzae, Flavobacterium, the gonococcus and F. funduliformis (see also Kheneberger 

 1942). Dienes (1943) and Smith (1942, 1943, 1944), have observed in Streptobacillus 

 moniliformis and F. funduliformis the formation from the bacterial ceU of " large bodies " 

 which may either segment and give rise to bacterial forms, or develop into colonies of 

 pleuropneumonia-like organisms ; and state that the large bodies appeared in some 

 cases to arise from the conjugation of two bacterial cells. 



We do not propose to enter into the vexed controversy over the existence of filtrable 

 forms of bacteria. The whole crux of the question seems to us to he in the definition of 

 the term " filtrable," and in the properties of the filter-passing bodies. Bacteria of the 

 same species are knoAvn to vary greatly in size under different environmental conditions 

 and at different stages of growth. That certain forms may be smaU enough to pass through 

 our relatively crude earthenware filters is hardly to be doubted, but whether these forms 

 differ in any of their essential properties from larger members of the same species, and 

 in particular whether they constitute some essential stage in the reproductive cycle of the 

 organism, is still undecided. In oiu" opinion the evidence that has so far been produced 

 does not suggest that they are differentiated in any important respect other than size, 

 and probably this differentiation is of a continuous rather than a discontinuous type. 



The Formation of Cell- Aggregates, — When a bacterial cell divides, the two 

 daughter cells may at once part company, or they may remain attached to one 

 another by their cell-membranes. When this incomplete separation persists 

 during many successive cell-divisions, cell-aggregates are produced, the form of 

 which will depend upon the planes in which successive divisions take place, and 

 upon the number of cell-divisions which occur before the cell-aggregate begins to 



