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Electron Microscope Study of Sections of Two Rat Liver Tumors^*

A. F. Howatson and A. W. Ham

( Department of Anatomy, University of Toronto, Toronto 5, Canada)

Sections of two rat liver tumors were studied with the electron microscope. The chief differences observed between the fine structure of the tumor and normal liver cells were in the nucleoli, ergastoplasm, and mitochondria. Nucleoli were very prominent in both tumors, but organized ergastoplasmic structures were scanty, appearing mainly in the form of vesicles. Both tumors, however, exhibited a substantial content of ergastoplasmic granules. The number of mitochondria per tumor cell was only about one quarter the normal cell complement. In the Novikoff tumor they exhibited very prominent internal membranes and varied in diameter over a greater range than those of normal liver cells. Some degenerating mitochondria were seen in a small percentage of the cells of the Novikoff tumor. The findings suggest the possibility of a relationship between organized ergastoplasmic structures and specialized cellular activities, associated with the differentiated state, on the one hand, and cytoplasmic granules and cell growth on the other.

^* This study was aided by a grant from the National Cancer Institute of Canada.

British Empire Cancer Campaign Exchange Fellow.

Received 8/ 9/54.