202 PROTISTS AND DISEASE 



In some minds will arise the question " What about 

 khangri-pots and tar ? " Cancers induced by such means 

 should be examined carefully. If they are of the same 

 nature as common spontaneous cancer, they will be found 

 to contain plassomyxes ; and the only conclusion that can 

 be drawn will be that these two agents are favourable to 

 the establishment of that particular relationship between 

 tissue cells and parasites that constitutes common human 

 cancer. 



And Cohnheim's embryonic rests ? Where such rests 

 really exist their cells may function in producing for us 

 internal secretions ; when they are the seat of cancer it 

 means that certain plassomyxes have found them to be 

 suitable hosts. 



Metastasis. It is usually assumed that the only way 

 by which a secondary malignant tumour can arise is by 

 metastasis, that is by the detachment of a portion of the 

 original tumour and development of the transplant in 

 another part of the patient's body. In sarcomas as, for 

 example, Fig. 46 ; 12, we see many parasites free in small 

 veins, therefore in such tumours secondary growths can 

 arise simply by the parasites finding elsewhere host-cells 

 similar to those of the original tumour. 



The mammary sarcoma referred to above is a granuloma, 

 and examination showed that the secondary growths arose 

 in all probability by migration of parasites. That meta- 

 stasis may occur in sarcoma is also seen in examining in the 



