528 THE BACTERIOPHAGE 



Such radial spreading could be accounted for by assuming that the observed par- 

 ticulate distribution of phage is only apparent and is due to its ready adsorption on 

 colloidal particles of the medium. This assumption is validated by experiments in 

 which the number of particles endowed with properties of phage in a given volume 

 of filtrate was altered, depending on changes in the composition of the medium/ It 

 was found that a slight increase in the consistency of the agar from i to 2.5 per cent 

 suppresses 99 per cent of visible plaques.^ D'Herelle accounts for this effect of agar 

 by stating that agar interferes with the diffusion of the metabolic products of the 

 Bacteriophagum intestinale, which in turn inhibits its growth.^ But until it has been 

 shown that Bacteriophagum intestinale possesses an independent metabolism, this ex- 

 planation cannot be accepted. 



Moreover, it is difficult to reconcile changes in the size of plaques as brought 

 about by various experimental procedures^ with the view of D'Herelle that the 

 plaques represent the "colonies" of bacteriophage. ^ For instance, if the size of the 

 plaque depends on the progress of "invasion" of bacteria by the parasite, then the 

 more numerous the susceptible bacteria are around the initial particle of Bacterio- 

 phagum intestinale the more of them should be "invaded"; each one of the invaded 

 bacteria in turn should become a source from which the next generation of parasites 

 would invade the nearest bacteria, ^ and in consequence the plaque should be corre- 

 spondingly larger. As a matter of fact, however, the greater the concentration of sus- 

 ceptible bacteria in the immediate vicinity of the original particle carrying the phage 

 (other conditions being constant) the smaller is the plaque.*" Similarly, it would be 

 difficult to explain on the basis of D'Herelle's hypothesis why both number and size 

 of plaques decrease with an increase in the proportion of old bacteria (which are not 

 subject to lysis), whereas an increase in the concentration of resistant bacteria leaves 

 both number and size of plaques unaffected.'' 



An explanation of all these phenomena can be given, if, instead of the hy- 

 pothesis of "invasion" of bacteria by the "obligate parasite," one takes account of 

 the tendency of the lytic agent to be adsorbed on agar, on old bacteria, etc. This 

 adsorption interferes with the progress of its diffusion. Since resistant bacteria do 

 not adsorb the lytic principle,^ other conditions being equal, the presence of an ex- 

 cess of resistant bacteria among the susceptible ones does not interpose an obstacle 

 for the normal diffusion of the lytic agent. 



' Nakamura, O.: ArcJi.f. Hyg., 92, 61. 1923; Doerr, R., and Zdansky, E.: ZtscJir. f. Ilyg. u. 

 hifcktionslzrankli., 100, 79. 1923. 



- Bronfenbrenner, J. and Korb, C: /. Expcr. Med., 42, 483. 1925; Proc. Soc. Exper. Biol, b' 

 Med., 21, 315. 1924. 



3d'Herelle, F.: The Bacteriophage and Its Behavior, p. 89. 1926. 



1 Bronfenbrenner, J.; and Korb, C: J. Exper. Med., 42, 483. 1925; Bail, O.: Arch.f. Hyg., gs, 

 I. 1925. 



sd'Herelle, F. : The Bacteriophage and Its Behavior, p. S-j. 1926. 



^Bronfenbrenner, J., and Korb, C: J. Exper. Med., 42, 483. 1925. 



'Meissner, G.: Centralhl. f. BakierioL, Orig., 93, 4H9. 1924; Kiniura, S.: Ztschr.f. Immunitiits- 

 forsch. u. exper. Therap., 45, 334. 1926. 



