20 Mr. J. C. Mottram and Dr. S. Russ. Susceptibility and 



third day they here form a definite band of growth. As the sarcoma cells 

 extend out into the reaction tissue, so fresh reaction tissue is formed more 

 distantly. 



2. The Microscopic Appearances of Grafts in Immune Animals. 



For this purpose, animals which had had two previous inoculations, with 

 negative result, were used. 



(a) The Appearances 24 Hours after Inoculation. — The reaction tissue 

 consists of an inflammatory oedema precisely similar to that seen in 

 susceptible animals. The sarcoma cells also present a similar appearance. 



(b) The Appea,rances after 48 Hoicrs {vide fig. 15). — The groundwork of 

 the reaction tissue is like that seen in susceptible animals ; fibroblasts, fat 

 cells, mast cells, blood-vessels, lymphatics, and polymorphonuclear leucocytes 

 have a similar arrangement. In contrast to these similarities, the arrange- 

 ment of the lymphocytes is strikingly different ; they are much more 

 numerous, and are especially abundant just external to the cleft, where they 

 form a solid ring of cells, encircling the inoculated emulsion. At the 

 periphery, plasma cells are to be seen near the blood-vessels. As in 

 susceptible animals, a few sarcoma cells are found outside the cleft ; the 

 vast majority, however, present degenerative changes ; they are oval or 

 circular in shape, their protoplasm is vacuolated, their nuclei are irregular 

 in shape and contain either no, or very few, fine chromatin granules, and a 

 central large irregular nucleolus. Whereas in the susceptible rat the 

 sarcoma cells external to the cleft are more healthy in appearance than 

 those internal, in the immune rat the reverse is the case. 



(c) The Appearances after 72 Hours (see fig. 16). — The lymphocytes have 

 increased in numbers, so that the solid ring of these cells, just external to 

 the cleft, is somewhat wider than in 48-hour specimens. Towards the 

 outer margin of the reaction tissue, an increased number of fibroblasts are 

 to be seen, and collections of plasma cells around the blood-vessels are 

 numerous. External to the cleft only a few degenerated sarcoma cells are 

 to be found ; no dividing sarcoma cells are to be seen. In some cases 

 degenerated sarcoma cells are seen to be embraced by large lymphocytes ; in 

 in other cases, nuclei or chromatin fragments are seen in vacuoles in these 

 cells. Degenerated sarcoma cells and chromatin granules contained in 

 vacuoles in large lymphocytes (macrophages), as seen in a graft in an 

 immune animal, but also in all cases where degenerative sarcoma cells are 

 disappearing. 



(d) I'he Appearances after Four to Six Days. — The sarcoma cells external 

 g to the cleft gradually disappear, so that, by the fifth or sixth day, not a 



