CARCINOMA OF THE THYROID IN SALMONOID FISHES. 5O5 



the fish. Macroscopically visible growths have not been seen in fish under about five 

 months of age. Anemia and cachexia, sometimes extreme in degree, are a frequent 

 but not constant accompaniment of the disease. Immunity is strikingly exhibited not 

 only among species, as the Scotch sea trout, but with given lots of a susceptible species. 

 Recovery or regression occurs when affected fish are removed from domestication to 

 wild conditions and also in fish in ponds in which the disease was acquired. 



VII. Feeding of fish tumors, or of human cancer, to brook trout has not during a 

 period of several months produced the slightest evidence of the disease attributable to 

 this feeding. The intimate association of susceptible trout with trout tumor material 

 in standing water, or with tumor fish in circulating unchanged water, has brought only 

 negative results. The fish tumor has not yet been successfully transplanted, but 

 implants have grown slightly and were alive at the end of three months. The tumor 

 extract is highly toxic to trout when injected into the thyroid region or subcutaneously. 



Wild brook trout brought from the wilderness and confined in cement tanks and 

 fed raw heart or raw liver have developed microscopic evidence of the disease by the 

 end of the first year, and visible carcinoma between the first and second year. The 

 feeding of cooked liver retarded the process. Spontaneous regression occurred in a 

 high percentage of the meat-fed fish by the end of the second year. Similar trout fed 

 upon marine fish, vegetable food, or a combination of mussels and live maggots retained 

 their normal thyroids. 



VIII. Either of the elements iodine, mercury, or arsenic dissolved as salts in the 

 ■water in which the fish are living interrupts the progress of the disease and restores the 

 thyroid epithelium to a condition approximating the normal. Recognizable effects are 

 produced within a few days. Visible tumors are markedly affected and may be much 

 reduced in size. Iodine and mercury are effective even when diluted by many millions 

 of parts of water. Iodine is effective when introduced into the digestive tract as well 

 as through the medium of the water. Negative results were obtained with thymol by 

 both these methods of administration. 



IX. The administration to dogs of mud and water from fish ponds in which thyroid 

 carcinoma was endemic gave suggestive evidence that the water and mud contained an 

 agent capable of producing marked changes in the thyroid. Scrapings from the inside 

 of old wooden fish troughs in which thyroid carcinoma was constantly produced gave 

 positive results. Four dogs were given for six months water to drink in which these 

 scrapings were immersed. All developed marked thyroid hyperplasia and three of them 

 enlarged thyroids. The thyroids of the three control animals remained of normal size. 

 Two of them were normal in structure while one showed slight evidence of hyperplasia, 

 probably referable to a previous experiment. 



Rats given for six months mud and water which had been taken from ponds in which 

 thyroid carcinoma was prevalent and transported several hundred miles gave negative 

 results. Rats given for four months water from the fish trough scrapings, also trans- 

 ported as above, produced results similar to those obtained with the dogs but less marked 

 in degree. 



8207° — 14 10 



