J. BRONFENBRENNER 543 



products accumulating in the culture with those variously assumed to be present by 

 different workers. There is also no explanation of the mechanism responsible for the 

 sudden onset and extremely rapid progress of autolysis of the culture. Besides, re- 

 peated chemical analyses of the cultures, after completion of lysis, have failed to in- 

 dicate any increase in protein split products which would be expected to take place 

 if bacteria were autolyzed.' 



The opinion of another group of workers is, therefore, that the disappearance of 

 the bacteria is not due to hydrolysis, but is the result either of a simple plasmolysis^ 

 or of a special, highly hypothetical type of cleavage not involving chemical disinte- 

 gration of bacterial cells.^ These authors offer no experimental evidence in support of 

 their views. 



Some light as to the nature of changes actually taking place in the bacteria under 

 the influence of the active agent seems to come from the direct observation of lysis 

 under the microscope. As has been mentioned earlier, D'Herelle has observed that 

 soon after the exposure of bacteria to bacteriophage the former begin to swell and 

 finally burst, due to internal pressure which he thought was exerted by the parasites 

 multiplying within the cells. ^ While the swelling of bacteria under the influence of 

 phage has been repeatedly observed by others,^ its constancy or its importance as a 

 factor in the disappearance of bacteria has not been generally accepted. The impres- 

 sion gained by several workers from observation of fresh as well as of stained prep- 

 arations is that only comparatively few bacteria undergo swelling, and that the great 

 majority of bacteria disappear without undergoing any visible change^ (Fig. 2). More- 

 over, it has been indicated that swollen bacteria do not end up by bursting,^ but, on 

 the contrary, they appear particularly resistant and disappear very slowly, if at all.'' 



However, the extent of the swelling of individual bacteria, the relative proportion 

 of swollen cells, as well as the actual relation between the swelling and the lysis, are 

 difficult to establish by direct observation alone; the swelling and the lysis go on 



'Weiss, E., and Arnold, L.: loc. cit.; lonesco-Mihaiesti, C: J. Exper. Med., 40, 317. 1924; 

 Zdansky, E.: loc. cit. 



= lonesco-Mihaiesti, C: loc. cit. 



i Some workers postulate the existence of a complex life-cycle in the development of bacteria, 

 during which bacteria may give rise either to functionally incomplete and not self-perpetuating ele- 

 ments ("spermites" [Hadley, P.: loc. cit.] or "ultraspores" [Rosenthal, L.: loc. cit.]) which possess all 

 the properties of bacteriophage. Others believe that bacteria may give rise to living, filterable frag- 

 ments which are capable of perpetuating this transformation by causing abnormally rapid growth 

 of the culture either directly (Nicolle, C: loc. cit.) or through the intermediation of ferments secreted 

 by them (Gamaleia, N. F. : loc. cit). 



•fd'Herelle, F.: Compt. rend. Soc. de bioL, 84, 339. 1921; The Bacteriophage and Its Behavior. 

 p. 115. 1926. 



5 von Preisz, H.: loc. cit.; WoUman, E.: Ann. de I'Insl. Pasteur, 39, 789. 1925; da Costa Cruz, 

 J.: loc. cit.; Zdansky, E.: loc. cit.; Manninger, R.: loc. cit.; Burnet, F. M. J. Path. &' Bad., 28, 

 411. 1925; Twort, F. W.: Brit. M. J., 2, 293. 1922; Hauduroy, P.: Compt. rend. Soc. de bioL, qi, 

 1325. 1924. 



'von Preisz, H.: loc. cit.; Manninger, R.: loc. cit.; Burnet, F. M.: loc. cit.; da Costa Cruz, J. 

 Compt. rend. Soc. de bioL, 95, 1501. 1926. 



7 WoUman, E.: Ann. ds I'lnst. Pasteur, 39, 789. 1925; Burnet, F. M.: loc. cit. 



*von Preisz, H.: loc. cit.; Burnet, F. M.: loc. cit.; da Costa Cruz, J.: Compt. rend. Soc. de bioi. 

 95, 1501. 1926; Gj0rup, E.: Thesis. Copenhagen, 1925. 



