X 



PROLIFERATIVE DISEASES OF THE 



RETICULAR TISSUE AND 



MESENCHYMAL CELLS 



In any discussion of the pathology of immunity a number of 

 conditions of malignant or semi-malignant character must 

 be included, and it is impossible to avoid some discussion of 

 the nature of malignant disease in the process. For reasons 

 which have been discussed elsewhere (Burnet, 1957) the 

 basic approach to cancer will be along the lines of those who 

 favour the somatic mutation theory. It will be advisable, 

 therefore, at this point to say something more about the 

 general concept of somatic mutation and its implications. 



I . Somatic mutation 



Geneticists agree that any genetic system, whether of man, 

 mouse, fruit fly or influenza virus, can undergo mutation. 

 There is every reason to believe that the chromosomes of all 

 somatic cells are as liable to mutation as those of the germ 

 cells. If this is the case it might be a reasonable guess that 

 10^ mutational events are taking place every day in the 

 somatic cells of the human body. 



Mutation by definition is an inheritable change taking 

 place at random amongst a population of organisms or cells. 

 It can affect the overall character of the population in which 

 it occurs only if it results in the appearance of a large enough 

 proportion of progeny with the new character. At the level 

 of the cell populations which make up the mammalian body 

 there are only three ways in which this can be accomplished. 



(i) The mutation occurs at a very early stage of embryonic 

 development in a cell which by the normal processes of 

 development and differentiation will have many descendants. 



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