454 BULLETIN OF THE BUREAU OF FISHERIES. 



Fifty clean domesticated yearling brook trout were placed in the closed circulation 

 with several badly tumored trout. In over four months, during a large part of which 

 the water was aerated artificially, without circulation, we did not succeed in producing 

 any notable thyroid reaction, and none which went beyond the controls. We do not 

 believe tumors can be produced by contact or association with tumored fish in this way, 

 at least not in any reasonable time. (See also feeding experiments p. loo.). 



The experiments in the closed circulation add to those in standing water in glass 

 dishes in showing that the pollution of the water by the fishes themselves and their 

 food refuse plays little if any part in the thyroid reaction. A number of trout were held 

 for 113 days in a 63-gallon aquarium tank with only four changes of water. Artificial 

 aeration was maintained by a constant air current liberated in minute bubbles at the 

 bottom of the tank. The fish were domesticated yearling trout, but not of a readily 

 susceptible lot, and none of them showed any external sign of thyroid change at the end 

 of the experiment. The fish were fed on liver, ate heartily, and were in good condition 

 thoughout the period. 



Most brook trout, however, held in troughs at the laboratory and suppHed with 

 Lake Erie water tended to acquire the red floor of the mouth when fed on liver. Such 

 trout kept in the ice-cold tap water in the winter and fed nothing, or given very low 

 feeding, showed within a few weeks signs of thyroid regression. Further evidence of 

 such regression is afforded by a yearling brook trout with a small but distinct thyroid 

 tumor visible at the isthmus. It was placed in a glass jar with standing water in the 

 cold and kept for 44 days without food. The water was changed several times. The 

 tumor had completely disappeared at the end of this period. 



TI^NSPLANTATION AND INOCULATION EXPERIMENTS. 



Several attempts to secure a new autonomous growth by implanting portions of 

 visible thyroid tumors in normal trout have been made. Both wild and domesticated 

 trout have been used. In only one fish have we met with partial success in that the 

 graft showed evidence of proliferation and was still alive at the end of three months 

 when examined microscopically. 



In December, 1908, a number of supposedly healthy fish were sent to Buffalo from 

 St. Johnsbury, Vt. These were inoculated in the thyroid region with a suspension of 

 thyroid tumors from fish obtained from Bath. The surface of the tumor was carefully 

 sterilized by burning. The greatest precautions were taken to prevent contamination. 

 The center of the soft tumor was carefully scraped out, rubbed up with salt solution, 

 and then injected. Nineteen fish were thus inoculated and later transferred to the 

 Bath hatchery, where they were kept in the troughs of the fish-hatchery building. An 

 examination of these fish in the autumn of 1909 showed that all of them had visible 

 tumors, but the epidemic of 1909 was at that time in full swing, and it was impossible 

 to determine whether the development of tumors was due to the inoculation or to the 

 simple fact that these fish had been placed in the infected water of the Bath fish hatchery. 



In a series of fish inoculated at Bath in the summer of 1909, in most of which the 

 grafts were contaminated and sloughed out, one fish (no. 83), which was inoculated Sep- 



