THE HISTOLOGICAL SIGNS OF RESISTANCE TO A TRANSMISSIBLE SARCOMA OF THE FOWL.

1. The living tissue of the chicken sarcoma, when implanted in susceptible hosts, survives, proliferates, and thus gives rise apparently to the whole of the new tumor. The histological findings about the graft do not suggest any other origin for the growth. 2. In fowls with a natural or acquired resistance, a very striking series of phenomena takes place about the graft or the established growth. They are referable to the presence of the living neoplastic cells and are essentially similar to those already described in mammals. 3. The lymphocyte has an association with the processes of resistance in the fowl, similar to, but more marked than that observed in mammals. 4. Resistance of the host does not constitute for the chicken tumor a differential means whereby the extrinsic agent present in the growth can be observed to engender it. In general, it may be stated that, when the new host is so unfavorable to the transplanted sarcoma cells as to cause their death, no tumor develops. 5. The activity of the extrinsic agent is negligible as affecting the interpretation of the phenomena about grafts of the avian sarcoma in resistant and susceptible hosts. They are referable to the presence of the transplanted cells. 6. The appearance or non-appearance of a specific, supporting, and vascularizing reaction in the host tissues cannot be looked upon as determining the fate of grafts of the chicken sarcoma. The same seems to be true of mammalian neoplasms.