DIGESTIVE ACTIVITY OF MESENCHYME 471 



and that supposed to have been developed in the embryo when 

 it was supphed with a small bit of adult lymphoid tissue. 

 "The lack of resistance seen during the early days of the incu- 

 bation period is replaced by a degree of resistance comparable 

 with that observed in the adult animal if the embryo is supplied 

 with a small bit of adult lymphoid tissue'' (Jour. Exper. Med., 

 1918, vol. 28, no. 1). But it is obvious that no analogy can be 

 drawn between an adult organism with its well-developed resist- 

 ance against heterogeneous grafting and an embryo into which 

 a small bit of lymphoid tissue has been introduced, for such an 

 embryo does not manifest resistance. The destructive power 

 of the adult splenic cell toward the Ehrlich sarcoma cell is the 

 attribute of an adult mesenchymal cell, just as general resistance 

 is an attribute of the adult organism. 



The digestive capacity of the adult splenic mesenchyme 

 toward the Ehrlich sarcoma cell, though interesting in itself, 

 cannot necessarily be connected with the natural resistance of 

 the host against heteroplastic grafting. It has not yet been 

 observed under ordinary conditions in animals naturally im- 

 mune or artificially immunized, the reported evidences of phago- 

 cytosis being confined entirely to dead tumor cells. The fact, 

 however, that this digestive capacity is called forth in the mesen- 

 chyme some time after birth and at the same time that the 

 general resistance is developed may ultimately prove to be of 

 great importance in a further analysis of the factors determining 

 the changes in the embryonic splenic mesenchyme and con- 

 ferring on it a digestive capacity. 



Though not necessarily having a causal relation to the natural 

 or artificially developed resistance of the organism, the mesen- 

 chymal digestive activity might be at least partly responsible 

 for it. As a tissue, the mesenchyme is the least difTerentiatied 

 and the collagenous fibers which it develops are not accumulated 

 within the cytoplasm, but are cast off outside. The cytoplasm 

 of an adult mesenchymal cell undergoes little change and may 

 never lose any of the fundamental properties of the cell, by 

 which I mean a further differentiative ability, proliferation, and 

 digestion of particulate matter as do many of the other cells of 



