444 VERA DANCHAKOFF 



arise, suggesting that a part of the chromatic material might be 

 furnished by the nucleolus. These changes of the tumor cells 

 within the allantois are especially suggestive in connection with 

 the work of Stevenson, 23. 24 ^j^q found a general lowering of the 

 vitality of tumors when grown on chick embryos for many 

 generations. 



The tumor grows in the above manner until about the seven- 

 teenth to eighteenth day of incubation, i.e., for ten to eleven days 

 and it may attain a diameter of 1 cm. and often reaches 5 to 

 8 mm. in thickness. • Occasionally tumor cells penetrate vessels 

 and small hemorrhages are found within the tumor; the tumor 

 cells here exhibit their ingestive and digestive power. Hemor- 

 rhages are usually followed by leucocytic infiltration and some of 

 the granular leucocytes may at the same time infiltrate parts of the 

 tumor. Leucocytic infiltration in a single tumor graft is not a 

 regular occurrence; it frequently takes place, however, in the 

 peripheral parts of the tumor, where a greater number of vessels is 

 present, especially in later stages. 



The growth of the tumor regularly stops at about the seven- 

 teenth day of incubation. Murphy believed that the develop- 

 ment of small lymphocytes in the host at this time furnished a 

 defensive mechanism against the further growth of a heteroplastic 

 tissue. But curiously enough, no small lymphocytic infiltration 

 can be found around the growing graft at this stage. 



While the tumor recedes necrotic zones appear usually in the 

 midst of the tumor tissue and gradually extend over larger areas 

 without marked reaction around them. No more indication for 

 a causal connection between tumor recession and the develop- 

 ment of small lymphocytes exists than for a connection with any 

 other aspect of the embryonic histogenetic processes. 



A thorough analysis of the changes in the allantois itself at 

 this period of development is important in connection with the 

 regression of the tumor. These changes affect not only a hetero- 

 geneous graft, but equally the growth of any graft, even that 

 of embryonal chick tissue, such as kidney, testis, and spleen, 

 which gradually become necrotic at this time. 



