Immunity of Rats towards Jenseris Rat Sarcoma. 23 



when accumulation of lymphocytes began, after which the sarcoma cells 

 disappeared. 



^/0.,5. : NO. 6. 



Fig. 17. — Shows tracings made with a projection micr9scope. Unshaded area — necrotic 

 centre ; shaded area — sarcoma growth, except in No. 2, where it represents lympho- 

 cytes ; dotted area — surrounding connective tissue. 



1. 5th day graft in a susceptible animal. 



2. 5th day graft in an immune animal. 



3. 5th day graft in a susceptible animal exposed to X-rays, 1^ hours. 



4. 5th day graft in an immune animal exposed to X-rays, 1^ hours. 



5. 10th day graft in a susceptible animal exposed to X-rays, 1^ hours. 



6. 12th day graft in an immune animal exposed to X-rays, 1^ hours. 



4. The Microscopic Appearances of Grafts in Animals Inoculated with 

 ^ Sarcoma Cells which have been previously Experimentally Altered. 



Grafts of a Mixture of Sarcoma and Spleen Emulsion Inoculated into 

 Susceptible Animals. — Two series of grafts were studied according as the 

 spleens from susceptible animals or from immune animals were used. 

 Experiments have shown that the inoculation of a mixture of tumour and 

 spleen resulted in delayed growth as compared with the use of tumour alone, 

 and that if the mixture be made with the spleen of immune animals, more 

 interference with growth results than when the spleens from susceptible 

 animals form the mixture (see figs. 10 and 11). 



A study of grafts under these conditions shows that very few sarcoma 

 cells are to be seen outside the cleft, until after the fourth or fifth day ; 

 during this period, there is some accumulation of lymphocytes in the 



