1. Multiple peritoneal sarcomas were observed in 163 or 59 per cent of the rats injected intraperitoneally with 1 cc. of an aqueous, saline, sucrose, or phosphate buffer suspension of washed, freshly ground taenia larvae obtained from rats of the same strain bearing an induced Cysticercus sarcoma. The average latent period was 152 days.

  2. At room temperature saline, sucrose, and phosphate buffer solutions adjusted to pH 7.2 and 7.4 made more stable suspensions than distilled water or phosphate buffer solutions adjusted to pH 6.6 to 7.0.

  3. Incubation of a saline suspension for 1 hour at 37° C., heating an aqueous suspension to 58° C., or storing the larvae at −70° C. for 2 or more hours destroyed all activity.

  4. The decanted supernatant fluid from an aqueous suspension of larvae centrifuged for 10 minutes at 2,000 r.p.m. induced peritoneal sarcomas, but no sarcomas resulted from the injection of supernatant fluid from similarly treated suspensions made with sucrose, phosphate buffer, or homologous serum. In most experiments the reconstituted sediment was as active as the original suspension. No tumors resulted from the injection of any supernatant fluid after it had passed through Seitz clarifying and sterilizing filter pads.

  5. Rats of a foreign strain did not develop tumors, and rats of the same strain as the host of the parasites that were injected when they were 12–30 days of age were no more susceptible than their older sibs.

  6. Larvae 6–10 months of age when removed from hosts with no visible primary tumor made inactive aqueous suspensions, but similar larvae 12 or more months of age made as active aqueous suspensions as larvae from hosts with gross Cysticercus sarcomas.

  7. No peritoneal tumors were induced by the intraperitoneal injection of the sediment from the fluid used for the final washing of the parasites or from the injection of the decanted supernatant fluid from an aqueous suspension of induced peritoneal sarcoma cells before or after passage through Berkfeld V or W filters.

*

This investigation was supported by grants from the American Cancer Society upon recommendation of the Committee on Growth of the National Research Council.

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