THE PARASITIC HYPOTHESIS 331 



of the micro-parasitic origin of malignant neoplasms. To urge 

 that in order to induce the aberrant growth there must be para- 

 sites within the parasites, is to pile Ossa on Pelion it is super- 

 erogatory. 1 



Nevertheless, these considerations, while demolishing the 

 argument based upon analogy, do not wholly do away with the 

 possibility that micro-parasites play some part in the production 

 of these and other malignant growths. There is yet another 

 method of approaching the subject. 



As I have already laid down in discussing the normal growth 

 of the syncytium, we have to see that there are two factors 

 constantly opposing each other the invasive powers of the 

 syncytial cells and the self-protective powers of the maternal 

 tissues. This is true, also, of the abnormal growth of the same. 

 It is possible, therefore, that the aberrant growth of the syncy- 

 tioma may depend not so much upon an exaltation of the invasive 

 powers of the component cells as upon a lowering of the self- 

 protective powers of the surrounding maternal tissues. Indeed, 

 the observations of Beatson and others, even if therapeutically 

 they have not been crowned with complete success, can only 

 be regarded as demonstrating that this second factor has to be 

 taken into account. Alteration of general metabolism following 

 upon removal of the ovaries does at times arrest malignant tumour 

 growth elsewhere. At the present time I feel even more strongly 

 than I expressed myself a year ago that it is along the lines of 

 research into the exaltation of the protective mechanism of the 

 organism, and into the diminution of the proliferative powers of 

 the tumour cells, that our energies should now be directed, and 

 coincidently I note that the last twelve months have not yielded 

 any more promise than showed itself then of distinct help to be 

 gained from this weary and unsatisfied hunt after specific cancer 

 parasites. 



I do not take the stand of denying the existence of such. In 

 this special connexion we can observe a parallelism between the 

 virulence of the microbe in bacterial disease and the protective 

 powers of the organism on the one hand, the invasive powers of 

 the cancer cells and the protective powers of the organism on 



1 It is worthy of note, further, that in the known cases where we have 

 intracellular parasitism e.g. coccidiosis we have no sign of the cells them- 

 selves taking on these parasitic functions. 



