544 



THE BACTERIOPHAGE 



simultaneously and continuously, and at different rates in the case of different bac- 

 teria in the same culture (Fig. 2). Moreover, the actual disappearance of individual 

 bacteria from the field of observation in fresh preparations is so sudden and rapid 

 that it is difficult to ascertain accurately the morphological appearance of each bac- 

 terium just prior to its disappearance. It is evident that such direct observations 

 must lead to highly divergent conclusions when carried out by different investiga- 

 tors, and even by the same investigator at different times.' 



Fig. 2. — A field of active bacteriophagy in early stages, showing simultaneous presence of nor- 

 mal bacteria, threads, and swollen bacteria. Stained with carbol-fuchsin, followed by methylene blue. 

 I'.astman K2 yellow filter. Magnification Xi,Soo. 



Fig. 3. — Granular appearance of the cytoplasm of threads. Stained with carbol brilliant green, 

 counterstained by fuchsin. Photographed through green filter. Magnification X 1,500. 



Fig. 4. — Swelling of bacteria and of threads. Stained with carbol-fuchsin, followed by methy- 

 lene blue. Photographed through green filter. ]\Iagnification X 1.500. 



The writer thought that an objective index of degree of swelling, and a 

 definite relation of swelling to lysis, might be established by a study of changes in 

 the relative volume occupied by the entire bacterial population as expressed in the 

 viscosity of the culture.^ These measurements have indicated that in about one or 

 two hours^ after the addition of bacteriophage to a heavy suspension of susceptible 

 bacteria, the viscosity of the mixture begins to increase slowly up to the time just 

 previous to lysis, when it reaches its maximum. About the time when clearing begins, 

 the viscosity of the mixture diminishes and in a comparatively short time reaches 



' von Preisz, H.: loc. cit. * Bronfenbrenner, J.: Proc. Soc. Expcr. Biol, o" Med., 23, 635. 1926. 

 i This interval varies with the concentration of phage. 



