NEUTRAL HEREDITARY INFECTION 



propagating proteins in the cytoplasm. Since the proteins in question 

 occur only in differentiated cells and are not transmitted in heredity, 

 we may regard them as analogous to a substrate-conditioned plas- 

 magene like the melibiozymasc of yeast. And in their relation to 

 the cell, their changes are analogous to the mutations of plasmagenes. 

 This is the basis of origin of cancer expressed in genetic terms. 



An interesting paradox now arises with regard to the treatment 

 of cancer. The cancerous cells owe their condition to a change in 

 their self-propagating cytoplasmic proteins. To break them of their 

 vicious habit we can do nothing directly. They are too numerous 

 and are, in any case, chemically self-adjusting. Reversion is unkno\vn. 

 Our sole remedy is to render their nuclei incompetent of supporting 

 cell life. This we do by breaking the chromosomes in the 

 resting nucleus (whose rapid development makes them singularly 

 susceptible) so that when it comes to divide its wrecked products 

 immediately die. X-rays or radium are the means of breakage. 

 (Koller, 1947.) 



The genetic analysis of the origin and transmission of cancer puts 

 us in a position for the first time to see and understand the triangle 

 plasmagene-cell-protein-virus, or (if you will) heredity-develop- 

 ment-infection in its true perspective. Tumour formation indubitably 

 arises by mutation in the first instance, but its properties are in- 

 herently untestable by the techniques of breeding. The distinction 

 between the diffusible and the non-diffusible agent of tumour 

 formation, on the other hand, throws into relief the distinction 

 between the cell-protein which provides the basis of differentiation, 

 and whose diffusion must be prohibited or at least controlled, and 

 that which provides the basis of infection whose diffusion is 

 inherently out of control. Thus cancer research has some fundamental 

 importance: it lies at the meeting of the ways. 



Neutral Hereditary Infection 



The conflict between the requirements of heredity, development 

 and infection becomes less as the particle or determinant becomes 

 less decisive in its effect. L'Heritier and Teissier discovered in the 

 cytoplasm of Drosophila the most neutral and indecisive of all par- 

 ticles, and it has proved to have the ambiguity of transmission that 

 might be expected. 



215 



