CARCINOMA OF THE THYROID IN SALMONOID FISHES. 439 



The remainder of some 200 five-year-old brown trout referred to in the summer of 1908 

 as free from tumors were again examined closely and found to be in a healthy condi- 

 tion, showing no visible tumors. 



A distinct change, however, was found in the 4,000 brown trout from Caledonia, 

 which in 1 908 showed no evidences of visible tumors. This lot is described in 1 909 as 

 consisting of about 3,000 fish, now 2 years old, from 6 to 8 inches in length. These occu- 

 pied cement races 22 and 23. Owing to insufficient help, it was not possible to examine 

 all of these brown trout. However, it was possible to determine that the disease in this 

 lot was now well established. Forty-eight died or were picked out from the lot and found 

 diseased. This does not represent the total number of brown trout affected. Between 

 June and the end of September, among the fish which died from this lot, 43 are recorded 

 as having been examined and all showed visible thyroid tumors. 



The brook trout of the hatchery were yearling fish, between 700 and 750 in number, 

 kept in races 10 and n. A number of them were also kept in race 14 and in the large 

 pond. In race 16, wooden, were 100 brook trout from Cold Spring Harbor hatchery. 

 To these were added 56 wild brook trout from the Old Forge hatchery later in the sum- 

 mer. By the middle of June the epidemic among the brook trout was at its height. 

 These fish were examined a number of times and some of the affected ones were put 

 into the large pond and others into the small pond 15. On June 24 the fish in race 10 

 were examined and 72 affected fish put into the large pond. About i fish in every 3 

 was found with visible tumors. Race n contained 142 yearling brook trout. Thirty 

 affected fish were found in race n and placed in pond 15. 



The remainder, 112 supposedly healthy fish, were removed to wooden race 18. 

 This race is supplied with the water of springs C and F, and the Cold Spring Harbor 

 trout kept in this water having remained free from the disease it was hoped that by 

 changing the fish from race 1 1 , which did not yet show evidences of visible tumors, they 

 might be saved. On examining these fish in race 18 in September, 107 of the 112 were 

 found to have visible tumors. 



During the summer a large number of the brook trout in the large pond died. One 

 hundred and five of these were found to have visible tumors. Early in the spring the 

 large pond which in September, 1907, had been stocked with some 6,000 brook trout 

 fry hatched during that season and in which during the summer of 1908 a few dead 

 yearling fish were found with visible tumors, was again cleaned, the fish being tempo- 

 rarily transferred during this time. Some 200 of these brook trout, now 2 years old, 

 were estimated to have escaped with the overflow into the brook. This stream was 

 protected by a screen at the lower end of the hatchery and such fish as escaped 

 remained in the brook during the summer, here receiving no artificial feeding during 

 this time and enjoying conditions of freedom so far as ample space and lack of crowding 

 were concerned. That a large proportion of these fish were affected with visible tumors 

 was shown by the fact that during the course of the summer 105 died of the lot trans- 

 ferred to the big pond, all showing visible tumors, and to determine to what degree they 

 might have recovered under the new conditions an examination was made on Sept em- 



