VIkUSLS, PUOVIRUSES AND THE CONILICT OF SYSTEMS 



was a nucleus-controlled plasmagene mutation because it is not 

 transmitted by grafting. Now, if it were an innovation or a presence, 

 it might invade and be classifiable with the Abutilon principle as 

 a provirus. But what if it is due to an absence, a deficiency in a 

 necessary self-propagating protein which propagates itself too slowly ? 

 A deficiency could not well invade. Our classification for the time 

 being must therefore be one of convenience. 



And our difficulty is not so much to show the relationship of 

 plasmagene and virus as to make a distinction between them of any 

 validity beyond the requirements of their adaptation to heredity 

 and infection (Table 19). 



Taken together the two scries of observations and experiments, 

 animal and plant, show that all the general properties of the natural 

 and noxious virus have arisen under experimental conditions. The 

 special property of insect-carriage alone has not been demonstrated. 

 Nor will it be readily demonstrated until the number of experimen- 

 ters is comparable with the number of insects. We may say, therefore, 

 that the properties of the reproductive particle, which are combined 

 naturally in the plasmagene with heredity, and in the virus with 

 infection, may, in these artificial conditions, be seen stripped of such 

 accessories. Conditions produced by the CO2 test in Drosophila, by 

 carcinogens in vertebrates, and by grafting and breeding in plants, 

 demonstrate the two modes of origin of the natural virus: by 

 mutation and by transplantation. 



Nuclear and Cytoplasmic Systems 



The close relationship between plasmagene and virus enables us 

 to put the virus in its proper place in the scheme of things. But it 

 does much more. It enables us to put the different agents of heredity, 

 development and infection in their proper relationship. They all 

 depend on self-propagating particles. These particles have different 

 kinds of control over one another according to the systems in which 

 they are organized and the methods by which they are propagated. 

 These seem to be essentially of two kinds, the nuclear and the 

 cytoplasmic, distinguished from one another in their intrinsic 

 properties and separated from one another by a protective 

 boundary. 



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