Immunity of Rats towards Jensen's Rat Sarcoma. 31 



roughly concomitant with the local accumulation of the lymphocytes. It is 

 certain that the lymphocytes do not ingest the sarcoma cells until some 

 degeneration has taken place in the latter. 



The negative evidence {vide p. 16) in the search for a toxin in the 

 circulating fluids indicates that it may be manufactured locally by the 

 lymphocyte. There is also more direct evidence in that where for any 

 reason there is a delay in the local accumulation of lymphocytes, then the 

 sarcoma cells instead of degenerating remain healthy and proliferate even in 

 an immune animal, and it is not until accumulation occurs that growth is 

 controlled. Degenerated sarcoma cells in the absence of lymphocytic infiltra- 

 tion have never been observed, except in the necrotic centre of tumours, 

 where the degenerative changes are different and where lymphocytic 

 infiltration is not seen. It would appear for this reason also that lympho- 

 cytic infiltration is not a reaction to dying or dead sarcoma cells, or else it 

 would occur under such conditions. 



In favour of there being an association between the production of 

 immunity and the local accumulation of lymphocytes is the fact that in all 

 tumours of the disappearing and oscillating types great accumulation of 

 lymphocytes occurs, and this is associated with unsusceptibility. It would 

 appear therefore that without local accumulation of lymphocytes neither 

 graft destruction, tumour destruction, nor production of immunity can occur. 

 Finally, it may be again mentioned that the condition of immunity to the 

 graft has not in any respect been observed to be due to a failure on the part 

 of the host to supply the necessary connective tissue or blood supply ; but all 

 the evidence goes to show that the immunity consists of a positive action on 

 the part of the host. 



The above statement refers only to Jensen's rat sarcoma, for in the case 

 ■of mouse carcinoma Eussell (7) has shown that the failure of an inoculation 

 in an immune animal is to be ascribed to a failure on the part of the host to 

 supply the " specific stroma reaction." 



The Bearing of the Observations upon Malignant Disease in the Human Subject. 



Spontaneous disappearance of malignant disease in the human subject is 

 very rare ; there is, however, no reason to doubt the clinical observation that 

 occasionally growths, malignant in all their aspects, do spontaneously 

 disappear. Clinical study has also shown that in some cases, although the 

 tumour may not disappear, its growth is not continuously progressive, but 

 that sometimes growth is held in check or may even regress, though finally 

 proving fatal. There is, in fact, ample evidence to show that an active 



