Experiments were designed to determine whether or not the arterial distribution of secondary tumors can be accounted for by the mechanics of circulation and the consequent distribution of embolic tumor cells.

The tumor selected was the Brown-Pearce rabbit tumor. Suspensions of fixed and stained tumor cells were injected into the left side of the heart in 20 rabbits, and the subsequent distribution of the cells was determined by microscopic section. The number of embolic stained cells per square centimeter was calculated for the various organs. In another series of 23 animals, viable cells were similarly injected, and the distribution of resulting tumors was determined.

When the total number of stained cells reaching an organ was compared with the number of tumors in that organ, correspondence was only fair. However, if only those embolic cells that lodged in the capillaries were considered, correspondence was excellent. Thus, the greatest number of emboli per square centimeter was found in iris, pituitary, adrenals, and kidneys; the smallest number in muscle, thyroid, and spleen. The same frequency distribution was found for the tumors.

These results, with the tumor and species studied, are in agreement with the hypothesis that the distribution of metastases is adequately accounted for by the mechanics of circulation and the consequent distribution of embolic tumor cells. Inthe organs studied, the role played by local chemical “soil” factors is evidently a minor one, if it exists at all.

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This work was supported by a grant from the Division of Research Grants and Fellowships of the National Institutes of Health, Public Health Service.

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