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 (Lernaeopoda) , 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 
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. 77). 
CRAIG BROOK STATION: CONDITIONS AT THE BEGINNING OP THE INVESTIGATION. 
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 
