204 BACTERIOPHAGES 



the second half of the latent period there is a decrease in the 

 opacity of the bacteria and they become markedly granular. 

 Mature phage particles appear within the bacterial cell, more 

 numerous as time goes on. Also one may see objects, slightly 

 larger and less opaque than mature phage, which are probably 

 homologous to the "doughnuts" described by Levinthal and 

 Fisher (1952). At a still later time the infected bacteria are 

 disrupted and exhibit a ruptured membrane, a dense pile of 

 phage particles, and relatively little other bacterial substance. 

 Prominent features of the cells throughout this course of events 

 are large, opaque bodies, several hundred m^ in diameter, which 

 are referred to by the authors as bacterial mitochondria. The 

 properties of these large granules were reported by Hartman, 

 Mudd, Hillier, and Beutner (1953), When triphenyltetrazolium 

 chloride was added to a growing culture of E. coli, it was reduced 

 to formazan which stained these granules red. They remained 

 stainable and unchanged in location or size throughout the pe- 

 riod of phage multiplication, even while the bacterial nuclei were 

 disintegrating and the bacterial cells were filling up with phage 

 particles. Quantitative studies indicated that the tetrazolium- 

 reducing activity of an infected bacterial culture remained con- 

 stant throughout the latent period and only decreased when 

 lysis began. Even after the bacterial cells had lysed, the red- 

 stained granules were readily visible in the microscope. These 

 granules are, according to these workers, functionally analogous 

 to mitochondria in the cells of higher organisms, and much cir- 

 cumstantial evidence suggests that they play an essential role in 

 phage multiplication. 



A technique likely to have extensive and useful application in 

 the future is the sectioning of fixed bacteria embedded inmethac- 

 rylate (Birch-Andersen, Maal0e and Sjostrand, 1953; Kellen- 

 berger, Ryter, and Schwab, 1956). Preliminary results with 

 T4 and E. coli B indicate that this may become a powerful tool 

 for following the course of intracellular events in infected bac- 

 teria (Maal0e, Birch-Andersen, and Sjostrand, 1954). Log 

 phase cells of E. coli contain two or more large vacuoles, each 



