372 SESSION IV. DISCUSSION 



H. L. Fraenkel-Conrat (U.S.A.): 



I have been asked a question and I should like to answer it. 



I have been asked about the ionic strength of the pyrophosphate which has a protective 

 action on nucleic acid, and attention has been directed to the fact that high ionic strengths 

 (greater than molar) may lead to the precipitation of nucleic acid. I quite agree with this. 

 We use molar salts for the precipitation of nucleic acids while oi m is the concentration 

 which protects nucleic acid from the dissociation induced by other salts. 



Now for Mr. Pirie's remarks. 



Owing to the shortness of time I must have expressed myself unclearly. From the virus 

 which had been destroyed by ultrasonic vibrations we obtained a nucleic acid, the mole- 

 cules of which, during sedimentation in the presence of salt, resembled nucleic acid from 

 the rods of virus which had not been destroyed. The activity of these acids, however, was 

 greater than one would have expected from the activity of the preparation from which 

 they were obtained, but it was less than that of the nucleic acid of the original virus. 

 For example, if the activity of the virus destroyed by ultrasonic vibrations was i"o ofthat 

 of the original virus, then the activity of its nucleic acid was about o-i% of that of the 

 original virus. 



One short observation on the question of the transfer of information. It is clear that 

 the specific information for the production of the whole nucleoprotein resides in a specific 

 entity, namely the nucleic acid, and different strains of nucleic acid will produce different 

 nucleoproteins. I believe that even if we can argue as to whether viruses are alive or not, 

 still we cannot dispute the fact that viruses contain nucleic acid in which is inherent a 

 considerable amount of specific information. 



W. M. Stanley (U.S.A.): 



As a biologist I can understand Dr. Smorodintsev's difficulties. But as a biochemist I 

 cannot be answerable for the similarity between viruses and genes. The analogy between 

 them, which I described, is simply a fact. Transduction is an experimental fact. I suggest 

 that, as scientists, we should develop our ideas on the basis of such facts. I am in complete 

 agreement with Prof. Smorodintsev as to the exogenous nature of viruses, that is to say, 

 with the idea that viruses come from outside and are not already present within cells. 

 But I am afraid we are faced with such conditions that it is hard to prove experimentally 

 whether the virus developed within the cell or entered it from outside. 



I an rather surprised with Prof. Smorodintsev for maintaining that viruses always 

 bring about the destruction of the cell. He knows as well as I do that some viruses persist 

 for years in a host without destroying cells and that there are latent viruses, e.g. a potato 

 virus, which seems almost hke a normal component of the cell of the potato plant. At the 

 same time I agree with him in defining a virus as a pathogenic agent. 



L. A. ZiL'BER (U.S.S.R.): 



I should like to make a few comments on the papers we have heard today. 



The facts which demonstrate the possibility of resynthesis of the tobacco mosaic virus 

 and the infectivity of isolated nucleic acid are of tremendous interest. The existence of 

 such 'infectivity' allows one to draw many far-reaching conclusions of extreme importance 

 both in regard to the problem of protein synthesis and to that of the pathology of infection. 



The absence of intact virus in the preparations of nucleic acid prepared from tobacco 

 mosaic virus is vouched for by the very sober evidence brought forward in today's papers 

 by Fraenkel-Conrat and others. But is this evidence enough to allow us to maintain cate- 

 gorically that protein is completely absent from the 'infective' preparations of nucleic 

 acid ? It seemed to me that it would be useful to study this question by using the method 



