DIGESTIVE ACTIVITY OF MESENCHYME 463 



The phagocytic and digestive activity of the adult splenic 

 mesenchyme has been shown to be, in double mixed tumor- 

 adult spleen grafts, the factor of growth restraint or rather of 

 active destruction of two rapidly growing tumors — the Ehrlich 

 sarcoma and tumor 180 (fig. 10). The activity of the mesen- 

 chymal cells brings the Ehrlich sarcoma to a rapid disappearance 

 and slows the growth of the 180. The splenic mesenchyme up to 

 the second week after hatching fails to manifest any phagocytic 

 activity against the heteroplastic mammalian tumor cell in mixed 

 tumor spleen grafts. In such grafts the mesenchymal cells do 

 not necessarily approach the tumor cells, neither do they form 

 capsules around them. The results of the two series of experi- 

 ments are invariably strikingly different: complete disappear- 

 ance of tumor in the tumor-adult spleen grafts and practically 

 unhampered growth in tumor-embryonic spleen grafts. Since 

 the process of encapsulation and digestion by the adult splenic 

 mesenchyme, in contradistinction to the embryonic tissue, 

 seems to point to an acquisition by the adult splenic mesenchymal 

 cell of a new property lacking in the embryonic splenic mesenchy- 

 mal cell, further knowledge as to this fact will be gained by 

 an analysis of other means tjapable of bringing about the 

 same effect. 



In these two series of experiments, the same tumor tissue is 

 mixed with splenic tissue in two different developmental stages. 

 As seen from the work of Sherman, ^^ the embryo contains at 

 different stages very varying amounts of lysins, opsonins, and 

 complement. The tissue of the adult spleen might, therefore, 

 contain outside its living cells certain substances injurious for 

 the tumor cell, while the embryonic spleen might not contain 

 such substances. Such a possibility cannot be denied without 

 further investigation. If this be the case, the prime factor in the 

 disappearance of the tumor in the double tumor-adult spleen 

 grafts would consist not in a new property of the adult splenic 

 cell, but in some extracellular substances present in the adult, 

 and lacking in the embryo which might produce a change in the 

 heterogeneous mammalian tumor cell and make it more accessible 

 to the phagocytic activities inherent in any mesenchymal cell. 



