IMMUNITY AND THE POWER OF DIGESTION. 2O5 



an intracellular digestive capacity. And this capacity is surely 

 not lost during the development of the embryo, at least the 

 mesenchymal cells continue to exercise this faculty, and wher- 

 ever cells in the developing organism have lost their normal 

 correlation with other tissues, as for example, red blood corpuscles 

 during the rearrangement of vessels, mesenchymal cells are seen 

 to ingest them and digest them within their cytoplasm. The 

 mechanism of this digestive activity is analogous to that observed 

 in unicellular organisms. Enzymes are not given off as in the 

 digestive tract, they work within the cytoplasm, they are endo- 

 enzymes. To a digestive activity of the mesenchymal cells is 

 due the disappearance of aseptic emboli, trombi and infarcts; 

 small sequesters may be entirely resorbed and catgut sutures 

 disappear in the organism in a short time. 



An intracellular digestive activity is exhibited in an intense 

 way by the tissues of embryos developing from mesoblastic eggs 

 in the early stages of embryonic development and only occasion- 

 ally during adult condition. This power is dormant in the 

 tissues of mammals during embryonic development, the embryo 

 receiving all the materials needed for its development in the 

 form of amino-acids from the maternal placenta, but is awakened 

 at the first opportunity of being confronted with unsplit protein. 



The digestive power of the tissues is well evident in respect 

 to cellular protein in the dead form. Only in a unicellular 

 organism did we see that their digestive activity confers on them 

 a power over living organisms and cells as well and therefore 

 becomes the source and the cause of their immunity against a 

 possible proliferation of the ingested organisms. May the 

 digestive capacity of the tissues of a multicellular organism, of 

 which we have seen a few examples, be also in some way con- 

 nected with the failure of a heterogeneous graft to take? Is 

 this power not the deleterious factor which cannot be overcome 

 by the grafted heterogeneous tissue and which inhibits its growth 

 and proliferation? 



The results of a long series of experiments, which I am going to 

 illustrate, show without any doubt that at least in some cases 

 it is the digestive activity of an adult mesenchymal cell which 

 inhibits the growth of a heterogeneous tumor or rather destroys 

 the actively growing tumor. The experiments were made with 



