T H E Cytology of the Tumor Cell I N T H E Rous Chicken Sarcoma

The cytology of the Rous chicken sarcoma No. I has attracted the attention of biologists since its discovery. Considered broadly, this study has been limited to that group of cells which responds in the animal body to invasion by foreign substances. This response to the tumor-producing substances from the Rous tumor, modified by the normal developmental tendencies of the cells, results in a neoplasm which in its well developed stages consists generally of cells of spindle or stellate shape, of a fibroblast-like nature, though round cells of the monocyte type are also present. The origin of these cells has been studied in vivo only after the tumor anlage has been well established. The work is laborious and trying, for all fowls do not respond uniformly to the tumor agent. Sequence in developmental stages is difficult to obtain since the tumor-producing substances vary in activity and the fowl may show a reaction akin to resistance. The use of intravitam dyes as an aid in identifying certain cell types adds another difficulty, for these stains, while serviceable, may produce toxic or even lethal effects. Added to these difficulties are those more fundamental barriers to a proper interpretation of histologic preparations. At present the hematologists are divided as to the ontology of the various groups of cells that make up the reaction tissue induced by an invading foreign substance. There are at least three different well established views regarding the origin of these cellular elements. Most of our knowledge pertaining to the cytology of the Rous tumor is based on material observed in tissue cultures. I t appears, however, from a study of the voluminous literature, much of which is conflicting, that the cells in vitro are no longer parts of a tumor tissue, but merely subsisting isolated elements. The interactions of these cells as they exist in the body have to a large measure been destroyed. I t seemed obvious, therefore, that only by standard cytological methods applied to a systematic study of tissue in vivo could a possible solution of the complex problem be attained. The following is a report of a study of the Rous chicken sarcoma from a period shortly after the tumor-producing material is introduced into the body of the fowl to the time when the bird succumbs. The various problems involved in the Rous tumor have been reviewed separately in a number of papers. Foulds’ (40) critical review deals with many of the important phases of this study. Here it will be necessary to refer only to those papers which have a direct hearing on the cytological origin of this neoplasm and the behavior of the cells involved. ’ Aided by grants from the Chemical Foundation and the International Cancer Research Foundation.