270 APPENDIX A 



however, such tumours resulted from a definite parasite, 

 we should look for a repetition of the original histological 

 structure. From the point of view of endocrine action, 

 however, nothing is more likely than that the subjects of 

 the experiment should break down in different ways. One 

 mouse cannot have the exact resistance of another, nor 

 could we look for the same results in all of them any more 

 than we should expect soot carcinoma in every chimney, 

 sweep. 



It must be insisted on that the developmental theory 

 of cancer is as definitely against cancer propagation by 

 transplantation of cells from one patient to another as it 

 is against a definite cancer parasite. When Shattock 

 endorses Paget's view that malignancies in families is not 

 due to such causes it is impossible not to agree. But 

 such an agreement by no means reduces us to the necessity 

 of admitting infection. A family with inherited tissue 

 instability, if exposed to conditions likely to decrease 

 health and further impair tissue balance, may experience 

 any form of malignant growth. Quite independent of 

 such diseases families can be found in which one member 

 is hyperthyroidal, another an athyroidal dwarf, and an- 

 other myxedematous. That families subject to malignant 

 disease die of various forms of it is distinctly against 

 parasitism. 



It is argued that some of the phenomena of radium 

 and X-ray malignancy imply a second factor, probably, 

 or at least possibly, a parasite. But in X-ray cancer 

 nothing more appears to be needed than the disturbing 

 effects of the rays themselves. It is difficult to suppose 

 that any organism is always infected with an organism 

 ready to display its activities on X-ray excitation ; a 

 supposition which is necessary as such rays, if sufficiently 



