CARCINOMA OR THR THYROID IN SARMONOID FISHES. 
467 
time being i : 32,000,000 parts. From this strength dilution rapidly occurred, reaching 
infinity in about four hours, the time required for the replacement of the water contents 
of the trough containing the fish experimented upon. The iodine was administered 
twice daily, morning and evening, so that there were long periods during which the fish 
received no iodine. The temperature of the water remained quite constant at 19.5° C. 
These fish were fed raw beef liver. The longest period of administration was 30 days. 
The fish employed were 15 clinically clean brook trout yearlings and 5 small tumor 
brook trout yearlings. No special controls were employed for this experiment, com- 
parisons being made with the controls for the previous iodine experiment. Here again 
some macroscopic evidence of regression was furnished by diminution in size of tumors. 
A brief resume of the microscopic study is given in table xi. 
Experiment 4 . — A small number of fish were tested for the toxicity of iodine admin- 
istered as Lugol’s solution into the stomach, and it was found that yearling trout will 
endure as much as i to 5 mg. and adult trout as much as 10 mg. A number of fish were 
treated, some of them during a period of 21 days, with injections into the stomach of 
Lugol’s solution containing from 1.16 mg. to 3.75 mg. iodine. Some of these died, 
probably through the cumulative effect of the iodine. Definite reduction of tumors 
was observed. Microscopic evidence of regression, although in the main not as marked 
as that occurring in other methods of treatment, is nevertheless definite. 
Experiment 5, showing the influence of mercury (table xii). This experiment is 
comparable with experiment i showing the effect of iodine administration. Mercury 
was administered as HgCk, under constant flow, in a dilution of i : 5,000,000 of mercury. 
The following fish were subjected to this treatment: Fifteen clinically clean yearling 
brook trout, 5 brook trout showing red floors, and 3 brook trout with tumors. Parallel 
controls receiving no mercury were employed. Fish were killed and preserved at fre- 
quent intervals, the longest duration of treatment being 30 days. The experiment was 
begun August 13, 1910. The temperature of the water was 20° C. ; feeding, the same 
as for other experiments. Here, also, macroscopic evidence of regression was furnished 
by clearing up of red floors and diminution in size of tumors, and in the almost complete 
clinical disappearance of a tumor yX mm. in diameter. A brief summary of the results 
of microscopic study is given in table xn. (Fig. 102, 103, 104, 105, 107, 108.) Three 
days is insufficient to affect tumors. In one case, however, after three days in 
I : 5,000,000 the fish was placed in i : 300,000 and was killed by the mercury in three 
and one-half hours. The epithelium showed great reduction. (Fig. 106.) Another 
after three days in i : 5,000,000 and 2.75 mg. of HgClj introduced into the stomach on 
the second day showed no reduction. 
Experiment 6 (table xiii). — Intermittent administration of mercury as HgCla) 
camparable to experiment 3 (intermittent administration of iodine). Mercuric chlo- 
ride was introduced into the water of the trough containing the fish experimented upon 
in such quantity as to make a solution, for the moment, representing i part of mercury 
in 38,600,000 parts of water. This was done twice daily, at 10 a. m. and 4 p. m. The 
dilution was estimated to have reached infinity in four hours. Five tumored brook 
trout and 10 clinically clean landlocked salmon were subjected to this treatment for 
periods of 15, 31, and 43 days. 
With this high dilution of mercury, even at the end of 43 days there was no definite 
macroscopic evidence of reduction in size of any of the tumors. The histologic study of 
the 15 fish of this experiment, together with i tumor and i clinically clean control, 
appear briefly summarized in table xiii. Of the 15 fish subjected to treatment, 5 
show distinct evidence of regression, either in thyroid hyperplasia or tumor; 2 show 
slight regression; 2 are doubtful; and 3 show no evidence of change. 
