60 BACTERIOPHAGES 



in a coliphage by Fischer (1950). The heat resistance increased 

 on rapid subcuhure and decreased on storage at room tempera- 

 ture. It may be related to the cofactor independence of nascent 

 phage T4 (E.-L. Wollman and Stent, 1952). 



11. Hydrostatic Pressure 



The effect of high pressure on the heat stability of phages was 

 investigated by Foster, Johnson, and Miller (1949). Pressures of 

 10,000 pounds per square inch were found to increase the stability 

 of phages Tl , T2, and T5, but to accelerate the inactivation of 

 phage T7. The change of velocity constant for inactivation of 

 phage T5 with changing pressure indicated that thermal inacti- 

 vation of this phage was characterized by a volume increase of 

 activation of 113 cubic centimeters per mole. This is the type 

 of effect usually found in protein denaturation. 



12. Osmotic Shock 



The production of ghosts from phages T2, T4, T6, and K by 

 osmotic shock, first described by T. F. Anderson, has already 

 been noted in Chapter IV. The phenomenon shows that 

 phages are rapidly penetrated by simple electrolytes, glycerol, 

 sometimes by sucrose, and even more rapidly by water. Sudden 

 reduction of salt concentration presumably causes water to enter 

 the particle until the membrane ruptures, permitting the internal 

 contents to leak out more or less completely. Gradual changes 

 in salt concentration do not have this effect (T. F. Anderson, 

 Rappaport, and Muscatine, 1953). 



Purely mechanical considerations suggest that the principal 

 damage should occur to the membrane of the head and this 

 seems to be so, since the tail structure of the ghost remains 

 morphologically and functionally intact (Herriott, 1951a; 

 Kellenberger and Arber, 1955). The same considerations 

 probably explain in part the resistance of the smaller phages 

 Tl, T3, T5, and T7 to osmotic shock (Anderson, 1949). Other 



