That there is a filterable agent concerned in the growth of malignant tumors of mammals has been indicated for the living animal by the work of Burrows (1, 2) and of Bisceglie (3, 4). The former, working with rats, found in a small proportion of his attempts that rat embryo tissue of 15 and 16 days development, comminuted and inserted into adult rats of the same descent after being immersed in the filtrate from the Jensen rat sarcoma, took the form of sarcomatous growth. In a much larger percentage there was evidence of stimulated proliferation without, however, the development of malignant tumor. Bisceglie carried on similar experiments with chick embryos of 2 to 5 days development, which, comminuted and injected into adult chickens along with the filtrate from a mouse carcinoma, developed into sarcoma. He also has found evidence that the preliminary injection of tumor filtrates greatly enhances the malignancy of inoculated neoplasms. In addition, Rhoda Erdmann (5) has reported the development of transferable tumors in animals which had been injected with tumor filtrate after disturbance of the reticuloendothelial system by the injection of India ink. Similar tumors developed in a few of her control animals without the preliminary treatment. Her work was done with filtrate of the Flexner-Jobling tumor, on closely inbred rats of apparently high susceptibility to that tumor (6).

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