PREFACE 11 



In the first place, it may be said that there are 

 two main theories regarding the cause of cancer, 

 both of which appear to involve the idea that 

 normal cell-division is an inherent vital function 

 of the cell. All living matter is capable of 

 reproducing itself, a fact which is so obvious that 

 it appears to be taken for granted that repro- 

 duction is an intrinsic function of living matter, 

 similar, for instance, to that of the assimilation of 

 water or the power of movement ; in other words, 

 that there is no actual exciting cause which 

 normally makes a living cell reproduce itself, 

 but that the living protoplasm will continue to 

 multiply automatically, so to speak, so long as it 

 is alive. 



With regard to malignant proliferation, how- 

 ever, one of the theories suggests that cancer is 

 due to a perversion of this normal function owing 

 to some unknown change occurring in the 

 intrinsic characteristics of the cell itself ; the 

 cell no longer reproduces itself in a normal 

 manner, but suddenly becomes excessively pro- 

 lific, and produces offspring which also multiply 

 very rapidly, exhibiting the well-known appear- 

 ances of " cancer cells. " The other theory leads 

 one to believe that the abnormal cell-division is 

 caused by the presence in the neighbourhood of 

 the cells of a living parasite introduced into 

 the body from without. It appears that many 

 investigators of the first theory consider it inadvis- 

 able to make a frontal attack, because they do not 

 hope to solve the nature of a vital function of 

 protoplasm, but are trying to find out what 

 will influence the growth of masses of cells or 



