SONIC AND OSMOTIC EFFECTS ON VIRUSES 179 



Freezing and thawing of infected bacteria also rendered the DNA 

 vulnerable. 



These experiments, therefore, strongly suggest that there is a 

 protective coating of protein around the nucleic acid, which is 

 broken by absorption to nonfunctioning bacteria but is suj)- 

 planted by some other cellular protection when the bacteria are 

 metabolizing. 



To check this, Hershey and Chase studied the fate of S^^. They 

 showed that all the S^^ is contained in the osmotic ghosts and is 

 in the antigenic part of the virus. They further showed that, 

 after virus attachment, violent agitation of the infected bacteria 

 releases 75 % of the S"' and only 15 % of the P^-, while still leaving 

 some agent inside the bacterium capable of multiplication of 

 further phage particles. In any event, apart from such treat- 

 ment, it is found that less than 1 % S^' is found in the next gener- 

 ation of phage, in contrast to 30% P^^. 



The following remarkable picture of the nature of T-2 phage 

 emerges. The dry virus is approximately 20% nucleic acid and 

 80% protein by volume. According to Anderson, attachment is 

 by the tail, which can be seen to be wide and flat at the end. This 

 occurs by the dual method already described, and thereafter the 

 nucleic acid must in some way be pulled inside the bacterium, 

 possibly by a simple pressure difference characteristic of the 

 difference in physical state of the bacterium and virus. The 

 force due to a tendency of the surface to contract would be suffi- 

 cient for this purpose. The jn-otein coating, with the entire anti- 

 genic surface, is then left behind and can be shaken off without 

 particularly impairing the ability of the si)ecific phage DNA to 

 perform its function inside the bacterium. 



The resulting picture of T-2 phage is shown schematically in 

 Fig. 7.4. The nucleic acid is shown as a long, thin structure con- 

 tained both in the tail and in the head. This is attached to the 

 protein by presumably weak forces, but sufficient in strength 

 to hold the surface intact until contact with the bacterium is 

 made. In this figure, no attempt has been made to distinguish 

 between sulfur-containing protein and other, although it is only 



