CARCINOMA OF THE THYROID IN SALMONOID FISHES. 425 



this variety into the United States from Germany in the eighties. They have been con- 

 tinually inbred and no fresh stock has been added. The rainbow trout have been in 

 the hatchery for 25 years and have not had fresh stock added to them. Attempts to 

 maintain the American brook trout in this hatchery have been so unsatisfactory as to 

 have been abandoned of late years. This has been partly due to the prevalence in the 

 waters of the hatchery of a copepod parasite (Ivcmseopoda) , which does not affect the 

 brown and rainbow trout, but is very destructive to the brook trout. A few years ago, 

 however, 200 brook trout from the annual hatching were raised to the yearling age for 

 the purpose of exhibition at the State fair. In September, when these fish were lyi 

 years old, they were examined, and it was found that every individual, with the exception 

 of possibly a dozen, presented visible tumors, and they were for this reason discarded. 

 It would appear from this observation that the brown and rainbow trout in this 

 hatchery had gradually developed into a more resistant strain than the native brook trout 

 -when introduced and maintained under the conditions affecting the hatchery. That 

 this supposition is perhaps correct is shown by the fact that at the Bath hatchery the 

 adult brown and rainbow trout which came from Caledonia remained practically free 

 from the disease during the course of what may be spoken of as an epidemic outbreak 

 in the latter hatchery (p. jj). 



CR.'MG BROtJK ST.-\TION : CONDITIO.MS XT THE BEGINNING OF THE IXVESTIG.\TION. 



With the inauguration of a joint investigation by the Gratwick Laboratory' and the 

 Bureau of Fisheries, a report of the presence of thyroid disease in the various hatcheries 

 of the Government was obtained, and from among these Craig Brook, Me., was selected 

 for investigation. An examination at this station made by the superintendent between 

 April and May, 1909, disclosed in the 6,695 fish on hand 376 with well-developed tumors. 

 This hatchery has been under the continuous superintendence of Mr. Charles G. Atkins 

 for a period of some 40 years. It is well equipped and at the time of beginning our inves- 

 tigation was particularly suitable for the work owing to the unusual number of salmonoid 

 species kept there and the fact that it was well known as one of the best conducted fish 

 cultural stations in the country. The scientific accuracy of its management and the 

 unusual completeness of Mr. Atkins's records, which extended back over a period of 

 years and covered nearly every factor which the progress of the investigation suggested 

 to us as worthy of study, gave most unusual advantages for accurate analysis of the 

 conditions under which carcinoma of the thyroid had developed here. 



An investigation on the ground was undertaken by Dr. Gaylord, covering the months 

 of July, August, and September. A review of the conditions found at Craig Brook during 

 this first summer is contained in an unpublished report transmitted to the Commissioner 

 of Fisheries under date of November, 1909, and was reported during the same month at 

 the meeting of the American Association for Cancer Research. 



Our attention was immediately attracted to an arrangement of 19 ponds containing 

 yearling and 2-year-old fish. A careful examination of all the fish in these ponds during 

 the summer revealed the interesting fact that the incidence of the diesase increased 

 8207°— 14 5 



