THE STUDY OF CANCER 29 



mental investigation of cancer has revealed the fallacious nature 

 of all reputed analogies with known forms of infection, the 

 results obtained are essentially of constructive value. The cell 

 problems being attacked now were unapproachable five years 

 ago, as were also the relations existing between tumours and 

 the organisms bearing them. Having recognised fully, and 

 insisted from the outset of our investigations, that the repro- 

 duction of the lesions of cancer in normal animals by trans- 

 plantation differed from the development of the disease ab initio 

 in animals spontaneously affected, I have confined myself largely 

 to describing the growth of cancer in the soil provided by 

 normal animals, and to drawing some inferences as to the 

 conditions obtaining in the development of cancer. I have 

 shown that even in normal animals the soil plays an important 

 part, and a part which can be modified at will. I have indicated 

 that the soil may play an important part in the spontaneous 

 appearance of cancer in individuals. I have also shown that 

 the primary properties of cancer cells differ. Therefore the 

 circumstances associated with the development of cancer require 

 to be considered with reference to the two sets of factors last 

 mentioned. 



The extent to which the experimental method has already 

 deepened our knowledge of the properties of cancer cells and 

 of their relations to normal animals renders it probable, that 

 its further application will throw light on the conditions 

 underlying the association of the inception of cancer with the 

 senescence of tissues, and on the increasing frequency of the 

 disease as age advances, throughout the vertebrate kingdom. 



