1 



Immunity of Rats towards Jensens Rat Sarcoma. 25 



6. Comparison of Results. 



The facts which these investigations upon grafts have brought out may 

 be conveniently marshalled under (1) the role of the lymphocyte, (2) the 

 behaviour of the sarcoma cells, and (3) the reaction tissue of the host. 



(1) The Role of the Lymphocyte. 



In susceptible animals they are seen in the reaction tissue in small 

 numbers, making their appearance on the second or third day. 



In immune animals the reaction tissue is loaded with these cells from the 

 second and third day until the final disappearance of the sarcoma cells. 



Both these characteristic reactions are affected by alteration of the experi- 

 mental conditions along two distinct lines, namely, by changing the condition 

 of the sarcoma cell before inoculation, or by altering the rat's condition before 

 inoculation. 



(a) Changing the Condition of the Sarcoma Cell. — If the cell be killed by 

 heat before inoculation, no lymphocytic accumulation occurs in either 

 susceptible or immune animals. 



If the sarcoma cell be given an exposure to the /3- and 7-rays from 

 radium sufficient to prevent any proliferation, some lymphocytes accumulate 

 in the reaction tissue on the second, third, and fourth days. 



If the dose of radiation be just sufficient to prevent the growth of a tumour, 

 then in susceptible animals there is a great accumulation of lymphocytes 

 from the fifth day until the final disappearance of the sarcoma cells. 



If the dose be sufficient only to delay growth, then an accumulation of 

 lymphocytes occurs about the fifth day, but subsequently they disappear and 

 the growth of sarcoma proceeds as under normal conditions. 



If the sarcoma cells be mixed with spleen cells before inoculation, more 

 lymphocytes are found in the reaction tissue than when unmixed sarcoma 

 cells are inoculated into susceptible animals; but they are less numerous 

 than in immune animals. 



(b) Altering the Rat's Condition before Inoculation. — If rats be splenec- 

 tomised before inoculation, then in susceptible animals no differences were 

 seen. In immune splenectomised rats there is a decided delay in the onset 

 of lymphocytic accumulation ; it is not until the fifth or sixth day that they 

 are present in numbers comparable to that seen in unsplenectomised immune 

 animals on the second or third days. 



If immune rats be given six or eight inoculations of 0"05 c.c. instead of 

 two, then a similar delay occurs in the accumulation of the lymphocytes. 



If rats before inoculation be given a dose of X-rays sufficient to reduce the 

 number of white cells in the blood by about 90 per cent., then in immune 



