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BULLETIN OE THE BUREAU OE EISHERIES. 
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 1 13 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 supplied 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. 
TRANSPLANTATION 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- 
