THEORIES AND PROBLEMS OF CANCER 



PART III 



By CHARLES WALKER, D.Sc, M.R.C.S., L.R.C.P. 



Director of Research Department, Glasgow Royal Cancer Hospital 



Having considered prevailing views of the nature of cancer and 

 the experimental work carried out in connexion with them, it 

 is now possible to draw general conclusions. The most pro- 

 bable explanation of the behaviour of the cells of which 

 malignant growths consist is that owing to the operation of 

 some stimulus these are no longer subject to the co-ordinating 

 influence which, under normal conditions, regulates the relations 

 between the different groups of cells forming the body ; the 

 result is that the cancer cells live parasitically upon the organism. 



Experimental work shows that the only way in which cancer 

 can be transferred from individual to individual is by transplant- 

 ing living cancer cells but to be successful the transplantation 

 must be effected in animals of the same species ; it is most easy 

 in the case of animals of the same race or breed and is more 

 difficult in proportion to the distance of relationship even within 

 the same species. 



The parasitic theory — the theory that the disease is due to 

 a specific micro-organism — appears to be incompatible with 

 many of the well-known facts connected with cancer; though 

 many micro-organisms have been found in malignant growths, 

 it is evident that none of those described up to the present time 

 is found in all cancers and not in any other condition. 



It is now necessary to deal with the present state of know- 

 ledge as to definite causes of cancer. To put the case briefly, 

 cancer is known to follow upon prolonged and more or less 

 continuous irritation and inflammation. It appears that in 

 cases in which the irritation and consequent inflammation is 

 slight, it must be continued during years before cancer develops. 

 Chimney sweeps' cancer appears to be due to the creases in 

 the skin being filled habitually with carbon ; minute particles 

 of carbon make their way between and even into the cells 

 and cause a certain amount of cell proliferation, which, in 

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