INTEACELLULAR MULTIPLICATION OF BACTERIAL VIRUSES 245 



represent a special type of enzyme whose synthesis is induced specifically by 

 the infecting bacteriophage. Many of these opinions are based on the presence 

 in phage ly sates of lysins, or agents which are distinct from the phage particles 

 and which are themselves capable of inducing lysis of uninfected, heat-killed 

 bacteria (Sertic, 1929; Schuurman, 1936; Gratia, 1937; Panijel and Huppert, 

 1954; Maxted, 1957; Ralston et al., 1957). Since by virtue of the metliods used 

 in their detection, however, the action of these lysms must necessarily 

 resemble lysis-from-without, it has still not been shown what role, if any, 

 lysins play in lysis-from-within. Inasmuch as fragments of the intact phage 

 particle can also induce lysis-from-without (Herriott, 1951; Herriott and 

 Barlow, 1957), it is quite possible that some, or all, of the lysins are incomjdete 

 bacteriophages instead of the intracellular lytic enzymes (cf. Section III, A). 

 The fact that a high concentration of lysin is produced after development of 

 certain "defective" bacteriophages supports this view (Jacob et al., 1957). 

 It is not even clear what could be the substrate for the intracellular lytic 

 enzymes, since bacteriophage growth and lysis-from-within proceed more or 

 less normally in bacterial protoplasts, from which the cell wall, a priori the 

 most likely substrate and that most certainly involved in lysis-from-without, 

 has already been removed (Brenner and Stent, 1955; Mutsaars, 1955; Salton 

 and McQuillen, 1955). In any case, the initiation of the reactions responsible 

 for lysis-from-within appears to require not only infection of the bacterium 

 but also onset of intracellular phage development. This may be inferred from 

 the fact that bacteria do not lyse which have been infected with nonmultiply- 

 ing virus particles, such as ultraviolet-irradiated, or certain types of mutant 

 and host-modified bacteriophages (Luria and Human, 1950; Benzer, 1955; 

 Luria, 1953; Bertani and Weigle, 1953). The formation of infective progeny, 

 on the other hand, does not seem to be prerequisite for lysis-from-within, 

 for in the presence of the dye proflavine infected bacteria lyse at the normal 

 time without yielding any phage (cf. Section III, C, 2). In the course of 

 normal phage growth, the l\i;ic reaction seems to be initiated about halfway 

 through the latent period, since after that time a rapid degeneration of the 

 host cell sets in which leads to its lysis a few minutes later, even if further 

 phage multiplication is arrested by cooling to low temperatures or by 

 addition of such poisons as cyanide (Maal^e, 1950; Bentzon et al., 1951). 



There exists, however, a "natural" way in which the imminent disintegra- 

 tion of a phage-infected cell can be staved off at almost the last moment. 

 Doermann (1948a) discovered that if bacteria infected with one of the T-even 

 phages are superinfecfed with additional phage particles shortly before the 

 end of the normal latent period, then the appearance of progeny phages 

 delayed by several minutes and the over-all lysis of the culture, as reflected 

 by loss of its turbidity, is retarded by as much as an hour. This is the 

 phenomenon of lysis inhibition. When lysis-inhibited bacteria finally do lyse, 



