Marsh. — Food and Thyroid Tumor 17 



eries. Feeding which produces certain results under the 

 conditions at one place will produce quite other results 

 at some other place, where the water supply and other 

 component conditions are different. It may also be said, 

 that in introducing or experimenting with vegetable 

 feeding, to break off abruptly the meat feeding of adult 

 trout is to invite failure. It seems necessary to begin 

 with fry and to make the transition very gradual. 

 Whether fry could be made to thrive upon flour alone 

 from the very beginning of feeding has perhaps not been 

 put to the test and the chances seem against it, but surely 

 some one ought to try it. 



However well the feeding of flour serves the purpose 

 for which it was undertaken, neither the nature of this 

 food nor its cooking suffice to prevent the development of 

 thyroid tumors. The yearlings and the two and three 

 year olds exhibited growths typical of the disease both to 

 the naked eye and the microscope. The tumors, how- 

 ever, were very small and the percentage of fish affected 

 low, the progress of the disease being much restricted in 

 comparison with liver or other animal tissue feeding. 

 Since the tumors are so closely associated with liver feed- 

 ing, one might infer that possibly their origin in flour 

 fed fish is to be referred to those first few months of free 

 life, when they received the usual diet of beef liver paste. 

 But the tumor growth is progressive under the flour 

 feeding, and changes of diet which affect the thyroid do 

 so rather quickly. The adult fish with tumors had been 

 without liver or meat food since their first half year of 

 life. Such an inference is opposed to the results of feed- 

 ing experiments, and can not plausibly be made. 



It remains therefore to be proved just what are the 

 constituents of a balanced ration which will be efficient 

 to entirely prevent that relatively immense overgrowth 

 of the thyroid gland which shows as visible tumors, if 

 indeed there be any such combination of foods. Al- 

 though thus far among the salmonoids, marine fish as a 

 food has not produced any tumors, it has not been so 

 largely fed as other foods, and since sea bass in captivity 



