386 Fortieth Annual Meeting 



rangement of metabolism, or the life processes of the fish, 

 due to the changes which domestication and occasional 

 conditions in the life of wild fishes produces, is one of the 

 possibilities. One can imagine that too great a burden is 

 thrown upon the small thyroid gland and that it enlarges in 

 response to a demand. The parasitic theory of the origin 

 of tumors is entirely unproved but when it is applied to the 

 thyroid disease of fishes as an explanation it fits rather 

 better than any other. One may cite the increase of disease 

 in the lower of successive ponds draining in series, one into 

 another; the spontaneous recovery under substantially the 

 same conditions which cause the growth, the immunity of 

 some species, and different broods or strains in the same 

 species; its occurrence among wild fish; the effect of such 

 drugs as iodine and mercury, possibly acting antiseptically. 

 Thyroid tumor is chiefly a disease of domestication like so 

 many other diseases of fishes. But domestication cannot 

 be said to be the cause, though its conditions evidently 

 favor the development of the disease. The tumor develops 

 also among wild fish, as has been shown, and though rarely, 

 yet the specimens known show typical tumors of good size. 

 The essential cause of the disease occurs without as it does 

 within domestication but by the latter it is intensified, in- 

 creased in amount or virulence, raised in power, changed 

 from a latent to an active state, or in some way made to 

 develop tumors. As the crowding of fish — not necessarily 

 overcrowding — lessened water supply and artificial feeding 

 are the most distinctive features of domestication, these 

 may be inferred to be the secondary factors related to 

 causation — one or more of them. What this relation is it 

 is quite impossible to say at present. 



As with cancer and goiter in man, there are at present 

 no known remedies or measures which will definitely either 

 prevent the inception of the process or cure its developed 

 stages. To increase the water supply, reduce the number 

 of fish dealt with and feed more natural foods are practices 

 obviously having a tendency to combat the disease, since 



