CYTOLOOIGAI, CHANCES IN THE INFECTED HOST CELL 191 



different laboratories. An important development was the 

 demonstration by Delbrtick (1940b) that two distinct types of ly- 

 sis could be observed with the same phage-host system depending 

 on the multiplicity of infection. Under conditions of normal in- 

 fection there was no change in cell shape up to the moment of 

 lysis. In contrast, when the multiplicity of infection was of the 

 order of 200 phage particles per cell, there was a relatively rapid 

 swelling of the rod-shaped bacteria into an oval or spherical 

 shape which then slowly faded out. The latter process, termed 

 "lysis from without," was never accompanied by liberation of 

 viable phage particles. At intermediate multiplicities of infec- 

 tion part of the bacterial population would lyse by the normal, 

 productive bursting, while the remainder of the population would 

 suffer the unproductive "lysis from without." There has been 

 relatively little study in recent years of modes of lysis during 

 bacteriophagy and a comparative study of various phage-host 

 cell systems might well be rewarding. 



Observations of the lytic process in the dark field microscope 

 were first reported by d'Herelle (1921, 1926). "Au debut, I'as- 

 pect des bacilles est normal; apres quarante-cinq a soixante 

 minutes on voit des fins granules, de plus en plus nombreux, 

 dans I'interieur des bacilles, le nombre des bacilles avec granules 

 inclus augmente rapidement avec diminution parallele du 

 nombre des bacilles normaux." As the number of intracellular 

 granules increased the bacteria swelled, became spherical, and 

 burst, liberating the granules into the medium. The bacterial 

 debris, however, quickly became invisible in the ultramicroscope. 

 D'Herelle concluded that the highly refractile granules that he 

 observed inside the infected bacteria were actually the bacterio- 

 phage particles. He based this conclusion on two kinds of evi- 

 dence: there was always a parallelism in lysates between the 

 number of granules seen in the ultramicroscope and the number 

 of phage corpuscles determined by plaque count; and the num- 

 ber of refractile bodies counted per bacterium infected with the 

 Shiga phage under study varied from 15 to 25, corresponding to 

 an average: yield of 1 8 phage corpuscles for one particle inocu- 



