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



24 hours after inoculation the spleen and liver tissues are found to be 

 everywhere separated from the inoculated material by a zone of inflam- 

 matory oedema, and subsequently these tissues remain always separated 

 from the sarcoma cells by the reaction tissue. 



In immune animals, on and after the third day, collections of lymphocytes 

 and plasma cells are to be seen in the liver substance, up to a distance of 

 2'5 mm. from the graft (see fig. 16). In normal rat's liver only a few 

 lymphocytes and plasma cells are to be seen. Similar increase is seen in 

 the spleen when inoculation is there made in the case of immune animals. 



3. The Microscopic Appearances of Grafts in Animals which have been 

 Experimentally Altered hefore Inoculation. 



(a) Grafts in Animals the Day After the Bevioval of the Spleen. — The 

 appearances of grafts in susceptible animals were found to be similar to 

 those seen in unsplenectomised animals. In immune animals there is a 

 delay in the accumulation of the lymphocytes until the fifth or sixth day, 

 and, during this period, the sarcoma cells form a narrow band of growth 

 outside the cleft ; subsequently they die out. 



(b) Grafts in Immune Animals which have been given simultaneously Six 

 or Eight other Inoculations. — As in splenectomised animals, there is a delay 

 in the accumulation of the lymphocytes until the fourth or fifth day, and a 

 similar temporary growth of sarcoma. 



(c) Grafts in Susceptible and Immune Animals which have been Subjected to 

 X-Badiation before Inoculation. — Experiments have shown (see fig. 9) that 

 the inoculation of immune animals which have been exposed to X-rays for 

 1-^ hours resulted in the growth of measurable tumours, which persisted for 

 about two weeks. A study of the microscopical appearances of grafts under 

 these conditions showed that the reaction tissue and the behaviour of the 

 sarcoma cells, in both susceptible and immune animals, was exactly similar 

 to that which occurs in susceptible animals. A vascular connective tissue is 

 formed by the host, into which the sarcoma cells wander, divide, and form a 

 band of new growth around the central necrotic area. The growth in such 

 animals appears to be just as vigorous as in susceptible animals, as is shown 

 in fig. 17. After about fourteen days the growth becomes surrounded by, 

 and invaded with, lymphocytes, in a manner similar to that which occurs in 

 disappearing tumours (see p. 24). The tumours finally disappear. 



Another set of observations was made with animals exposed to X-rays 

 for half the time, namely, | hour. Measurable tumours did not result, but 

 a temporary growth of sarcoma occurred up to the fifth or sixth day. 



