Mesenchymal Activity in the Chicks. 



69 



The tumor begins to grow in such grafts in the form of small 

 foci surrounded by adult mesenchyme, the tumor cells assuming 

 the form of polygonal or fusiform bodies in a syncytial and even 

 plasmodial arrangement. Soon, however, in the region in which 

 both tissues come into contact, the tumor cells, whether in mitosis 

 or in the resting stage, become separated one by one from the 

 syncytium. Mesenchymal cells closely encircle them and form 

 around them a wreath of nuclei with a common cytoplasm, fre- 

 quently giving the impression of large giant cells with a tumor cell 

 within their cytoplasm. The tumor cell, at first closely surrounded, 

 is soon found to be situated in a vacuole, the cell itself diminishing 

 in size, gradually losing its structure, and finally completely disap- 

 pearing. A graft of Ehrlich sarcoma, though showing at first an 

 extensive growth, and in control animals reaching in 7 to 9 days a 

 size of 1 to 1.5 cm. in diameter, is generally brought by this process 

 to disappear five days after grafting. Not a single tumor cell 

 could be discovered under the microscope in full series of grafts, 

 though the identification of the large cells of the Ehrlich sarcoma 

 amongst the chick mesenchyme is rather easy. An absolute 

 biological proof of the destruction of the tumor cells could be 

 obtained by the inoculation of such grafts into mice. A similar 

 activity of the adult splenic mesenchyme, though affecting sar- 

 coma 180, was not sufficient to check completely this very fast- 

 growing tumor, and the tumor still grew in spite of a partial de- 

 struction easily demonstrable under the microscope. 



The process of separation of the tumor cells with their subse- 

 quent death and final disappearance of digestion, takes place on 

 the whole circumference of the tumor foci, if tumor and spleen are 

 thoroughly mixed together. If grafted separately but adjacent 

 to each other, the process develops only in that region in which 

 both grafts come into contact, and not on other parts of the cir- 

 cumference. If the grafts be separated by a considerable space, 

 the reaction will develop if, and at the time when, both tissues 

 come together. This reaction, therefore, depends not upon a 

 resistance of the host, which was supposed to be conferred by the 

 introduction into its organism of a bit of spleen with its small 

 lymphocytes, but upon the functional properties of the splenic 

 mesenchyme introduced. This process is certainly not a mechan- 



