CARCINOMA OF THE THYROID IN SALMONOID 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 HgCl2, 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 

 chnical disappearance of a tumor 7% mm. in diameter. A brief summary of the results 

 of microscopic study is given in table xii. (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 HgCl2; 

 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. 



