American Fisheries Society 389 



field is offered for conjecture and disquieting inferences 

 which are as impossible to disprove as to prove. 



What is the case that might lie against the salmonoids 

 in the matter of cancer, and how definite is the evidence in 

 support of it? It is that in some way, certainly indirect, 

 obscure and probably occasional or rare, fishes are a factor 

 in the cause of human cancer and aid in the spread or 

 transmission of this disease. Among the many theories of 

 cancer causation is that which ascribes the cancer process 

 to a living organism — a parasite. If this theory is finally 

 substantiated it will afford a case of parasitism radically 

 unlike all known forms of parasitic disease. It is only on 

 the assumption of such a parasitic factor in cancer that any 

 causal relation between fish and human cancer can be main- 

 tained. Now there are two general facts which appear 

 rather vaguely to bear an important significance. Atten- 

 tion has been frequently called in the medical profession to 

 a seeming relation of cancer to water. There is a consider- 

 able literature citing statistics showing a concentration of 

 cancer along water courses. It is evidently a fact that the 

 well-watered regions of the United States are favorite 

 cancer localities, rather than the drier or arid regions. It 

 is, of course, in these watered regions that fish thrive and 

 are artificially propagated and planted. It has been said 

 that a map showing the distribution of the chars and trouts 

 in this country would by the same tokens illustrate the dis- 

 tribution of cancer. This coincidence may be accidental but 

 the fact is interesting and suggestive. The other general 

 consideration is that the probable increase of cancer during 

 the last few decades has been simultaneous with the develop- 

 ment to large proportions of the artificial propagation of 

 the salmonoids. 



Now, no one suggests and it is not credible that any 

 case of cancer has been or will be caused by eating fish of 

 any kind. Cooked fish will transmit no disease and in this 

 country no one eats them raw, and even in that case no 

 transmission of cancer need necessarily be inferred. The 



