THE DIRECT EFFECT OF RADIATION ON 

 PROTEINS, VIRUSES AND OTHER LARGE MOLECULES 



Ernest C. Pollard 



Well, I richly deserve what I am getting today. In reading through the 

 very fine summary of last year's conference, I realize that I was operating with 

 a needle most of the time and it is very fair and just recompense for having 

 done this. Here I am in a position of putting up or shutting up and so I had bet- 

 ter talk about it. 



The work we have done at Yale had as its original interest the use of 

 radiation to study structure. This follows directly along the pattern set by Lea, 

 and we consider ourselves, if you like, descendants of Lea in our philosophy 

 and outlook in the way in which we seek to use radiation. The use we have made 

 of it has somewhat surprised us; some of the methods of using ionizing radia- 

 tion to study viruses have been summarized in my book. (1) 



Somewhat to my surprise and pleasure, one structure that we sort of 

 postulated for Newcastle disease looks very much like the electron micrographs 

 that are now being turned up in New York by Morgan et al (2). So there is evi- 

 dently satisfactory validity to this method of using radiation to study structure. 

 I am acutely sure it has limitations, and it would be very foolish to use it with- 

 out knowing these limitations. One of the reasons for this discussion today is 

 to send me away with a clearer idea of what the limitations are. 



In this work there is one basic aim; i.e. , to preserve the space rela- 

 tions of ionizing radiation. You use these space relations to tell you something 

 about the nature of the system you are studying. There is a second feature to 

 this: the ionizing events that occur must make some change in whatever you are 

 looking at. This change is, at the present, rather too inclusive. It involves, 

 as a rule, the removal of activity or some very vital change like that. It would 

 be preferable if the change were more moderate and could be studied in some 

 detail after it had occurred, because then we would get more information. 



Because space relationships have to be preserved, we have operated 

 almost entirely in the dry state. Everyone will ask, "How dry^", and the 

 answer that I can give to that question is in the following terms: 



First, the specimens are exposed in high vacuum, usually inside the 

 vacuum chamber of a cyclotron, so that the total vapor pressure goes down to 

 10"5 mm. Hg. 



