CHAPTER 10 



VIRUSES, PROVIRUSES AND THE CONFLICT 



OF SYSTEMS 



The Propagation of Viruses and their Getietics Animal Tumours 



Neutral Hereditary Infection The Origin of Viruses 



Nuclear and Cytoplasmic Systems 



Outside the nucleus there are, as genetic evidence has shown us, 

 reproductive bodies in the cell. The plastogenes we can distinguish 

 as bodies, which must He in the proplastids or the mitochondria. 

 These bodies can be stained differentially and they are proteins with 

 nucleic acid attached, sometimes combined also with phospholipids. 

 The nucleic acid is the ribose form, not the desoxyribose of the 

 chromosomes. Other bodies, "microsomes" 50-200 m^u, in diameter, 

 Claude has separated by centrifuging lung, pancreas and plant cells. 

 The ribose nucleic acid in the cell, whose quantity is correlated with 

 the rate of protein production, is largely localized on these bodies. 

 They, therefore, probably include both the plasmagenes and the 

 other self-reproductive proteins important in development and 

 differentiation. 



The Propagation of Viruses 



Bodies or particles also occur in cells which manifest heredity 

 in themselves, but do not determine it in the organism which 

 includes them; for, characteristically, they get where they are, not 

 through the egg or the spore, but by infection or invasion or even 

 the transplantation of tissues. The most obvious of these bodies are 

 the recognized viruses, parasites of animals, plants and bacteria. The 

 larger viruses are complex in organization. Vaccinia, for example, 

 contains tat, carbohydrate and even copper, as well as nucleoprotein. 

 It also contains desoxyribose nucleic acid. Its particles are about 

 150 lUfx in diameter. The simpler forms are also proteins, but they 

 usually have ribose nucleic acid attached to them. They exist in the 

 cell as particles, either globular and 20-30 m/x in diameter, or rod- 

 shaped, 15 mfjL thick and 125-1,000 m/x long. They may be separated 



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