Control rats and rats bearing multiple implants of Flexner-Jobling carcinoma were fed or fasted and the weight changes determined for tumors and normal tissues. Glycine-2-C14 was used to label the tissue proteins and to permit a study of amino acid exchange. Animals fasted 5 days lost 31 per cent of their body weight and 39 per cent of their liver protein. Tumors on such animals grew almost as rapidly as on fed rats. It was observed that in either fed or fasted rats, the specific radioactivity of the proteins and nucleic acids of normal tissues declined with time, as did the total radioactivity per organ. In contrast, the total radioactivity of the tumor proteins increased rapidly. It was concluded that protein metabolism in the Flexner-Jobling carcinoma is essentially, if not completely, a “one-way passage,”, and that the proteins of this tumor are not available to the host for fuel during starvation. It is suggested that the type of experiment described herein be used to survey host-tumor relationships for a variety of tumors, including some which grow more slowly and are less anaplastic than the Flexner-Jobling carcinoma.

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This research was supported in part by a grant from the American Cancer Society on the recommendation of the Committee on Growth of the National Research Council.

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