198 PROTISTS AND DISEASE 



in the mammary sarcoma ; and Fig. 55, 8 to 10 (chorio- 

 carcinoma), shows other similar forms. Such forms are I 

 think, alternative to the amoebula. Gaylord once met 

 with a definite spirochaete in mouse-cancer. I have no 

 doubt that, if regularly looked for, such instances would 

 be multiplied, but until it is generally recognised that the 

 spirochaete of syphilis is but one of a series of phases of 

 Cytoryctes luis, I do not think much can be gained by regular 

 search for spirochaetes in cancer. The infective sarcoma of 

 dogs in which Mettam found spirochaetes might be a useful 

 condition to compare with syphilis. 



Cultures of cancer-parasites. We must imitate nature's 

 ways if we are to succeed in cultivating certain organisms. 

 In the natural process the parasites of molluscum are 

 extruded and fall from the host : we should expect them to 

 develope in water, and so it is found to be by experiment. 

 Plassomyxa contagiosa produces broods of new individuals 

 outside their chief host, exogenously as it is termed. 



In cancer the parasites breed endogenously passing through 

 repeated cycles which end only with the death of the host. 



To imitate nature's way in cancer we must cultivate the 

 parasites in the tissues or fluids of the host and at the tempe- 

 rature of the host. Gaylord has used this method with success. 



We have seen, Chapter VI, that the commonest mode of 

 subdivision of Plassomyxa contagiosa is by the formation of 

 oil-like spheres, the protoplasm of which may circulate for 

 hours or days. 



