APPENDIX A 267 



infected it is, so far as its cells are concerned, obviously 

 in riotous health, and although symbiotic alliance occurs in 

 lower organisms such as Convoluta roscoffenis the sym- 

 biosis is not intracellular, as the infective, microbic, or 

 protozoal theory of cancer demands. 



Moreover, even if a special infection hypothesis were 

 proved to be correct, we should still have to seek the cause 

 of the tissues acting as they did when affected by, or in 

 symbiosis with, the pathogenic agent. Till that is under- 

 stood we are still in the dark, and the particular organism 

 which causes disaster remains no more than a secondary 

 or exciting cause. It is, therefore, strictly logical to 

 range all infection causes as irritative, or irritative and 

 weakening, agents, whether they be one or many. Lambert 

 Lack teaches that periodontitis is a common cause of 

 tongue cancer, by which he means that its toxic products 

 acting in combination with other irritation and syphilis 

 in some way urge the epithelium into revolt. Such a 

 view is logically sound. It is stated by Peyton Rous 

 that fowl sarcoma can be reproduced by the injection of 

 a filtered extract of the original malignant growth. It 

 is therefore inferred by some authorities that the repro- 

 duced disease is due to a filter-passing organism. So long, 

 however, as such a filter-passer cannot be cultivated, or 

 shown to exist by other methods, it is only legitimate to 

 infer that such a phenomenon must be ranged among 

 those caused by irritative agents or toxins pulling the 

 trigger of an unstable tissue. Moreover, even if the sus- 

 pected filter-passer is proved to exist, the only logical 

 inference to be drawn is that an infective organism can 

 excite sarcomatous overgrowth in the fowl's tissue just 

 as other irritative agents can produce carcinoma. The 

 evidence takes us no further than irritation. Even if it 



