162 APPLICATION TO CANCER RESEARCH 



consideration of carcinoma, for we considered that if we 

 succeeded in throwing any light on the causation of that 

 disease, it would be time enough for us to investigate 

 sarcoma. Cancer is much more common than sarcoma ; 

 but it has to be remembered throughout that, from 

 the similarity of the cardinal symptoms of the two 

 diseases, there is probably an intimate association 

 between the causes of both. The connective tissues 

 can become malignant at any age. The epithelial 

 tissues are usually attacked after the age of forty. 

 This age-incidence of carcinoma is most striking, and 

 it necessarily constitutes a fundamental fact with 

 which all our thoughts regarding the cause of 

 cancer must ultimately harmonize. It is a disease of 

 senescence; it attacks people when they are robust and 

 apparently in a state of highest vitality, just when they 

 are in the prime of life, or having just passed it. We 

 have to remember in this connection that the expres- 

 sion "prime of life" in its physiological sense may be 

 taken to refer to middle life that is, somewhere about 

 the age of 35; and we may further understand that 

 before that age a man is being built up, whereas after- 

 wards he enters upon the downward trend and steadily 

 progresses towards physiological death, which may be 

 taken to occur about the seventieth year. We may 

 therefore consider that the climax of his physiological 

 life is reached at 35. 



The age incidence of cancer is unique; there is no 

 other disease which has this limitation in its age 

 averages. Exceptions do occur, it is true, but the 

 number of cases occurring during senescence, when 



