160 The Nature of Biological Diversity 



postulated some years ago as required for the integrated hehavior of 

 cells — a patterned framework of surfaces and cavities upon which 

 enzymes could he differentially distributed and within which metaho- 

 lites and products of metabolism could he segregated. 



With this thought in mind, it is interesting to look at cells in which 

 at least one expression of normal integration — the capacity to form 

 normal tissues — is lost. These are the cells of tumors. 



Carlo Bruni and I have in recent years been comparing the fine 

 structure of rat hepatomas, possessing different growth rates, with one 

 another and with that of the normal liver ( Porter and Bruni. 1962 ) . 

 The hepatomas were all induced with chemical carcinogens, have gone 

 through many transplantations, and are cytologically stable. In terms 

 of fine structure, the cells of each tumor show characteristic features 

 which have been constant during the period of study. A number of 

 observations of interest could be mentioned, but in this connection it 

 is important to note only that the structure of the endoplasmic reticu- 

 lum is very abnormal (Fig. 14) and that the degree of departure from 

 the normal is most pronounced in the more rapidly growing tumors. 

 To what extent the lesions in the ER are involved in other manifesta- 

 tions of malignancy is hard to say, but, if in the normal the endo- 

 plasmic reticulum does play a role in the integrated biochemistry and 

 physiology of the cell, the form it shows in these hepatoma cells would 

 not be expected to support that role. 



References 



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