1. The morphology of Rous sarcoma in chicks made folic acid-deficient by means of diet or antagonist was compared to the alterations in the bone marrow and gastrointestinal tract.

  2. Similar comparisons were made with birds on a control diet, as well as on a folic acid-free diet supplemented with folic acid.

  3. The folic acid content of the tumor tissue and of the pectoral muscle (the tumor site) was determined by means of a bioassay in animals on the above regimes.

  4. Folic acid deficiency is associated with marked decrease in the growth of Rous sarcoma.

  5. This is characterized by a marked increase in the size of the tumor cell (nucleus and cytoplasm), hydropic swelling of the nucleus, and apparent concentration of the chromatin.

  6. These features are also seen in the immature cells of the bone marrow and the gland cells of the intestine of the deficient animals.

  7. Rous sarcoma contains considerably more folic acid than the tissues of the tumor site. This relationship is maintained even in the presence of folic acid deficiency or folic acid excess in the diet.

*

Presented in part at the Forty-seventh Annual Meeting of the American Association of Pathologists and Bacteriologists, Madison, Wis., April 14, 1950.

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