CARCINOMA OF THE THYROID IN SALMONOID FISHES. 435 



TABLE V. INCIDENCE OF THYROID CARCINOMA IN WOODEN TROUGHS, CRAIG BROOK, 1910-1912. 



o Many fish used in experiments. 

 LAKE AUBURN HATCHERY, MAINE. 



This is a State hatchery in Androscoggin County. In August, 1910, an examination 

 of fish for visible tumors was made and the general conditions inspected. Pond i was 

 a dirt pond fed by two springs of water very cold at its origin, and standing at 11 C. 

 in the pondon August 20. The spring water has a very low content of dissolved matter 

 and is said to have about the same analysis as the well-known Poland Springs of Maine. 

 The pond held nearly 400 brook trout of 3^ years of age, which had occupied the pond 

 since the yearling stage. They had been fed raw beef liver until a year old and raw 

 beef heart ever since. The fish were raised from eggs from the local station and from 

 domesticated eggs obtained from Michigan. They were apparently in fine condition, 

 were feeding well, and had suffered but little loss. One hundred and thirty-one of these 

 trout were examined, of which 20.5 per cent showed visibly diseased thyroids and 5.3 

 per cent of the 131 bore visible tumors. 



Pond 2 was a similar dirt pond, fed from six independent springs and sometimes 

 by the overflow of pond i. Its water was warmer, being 15.5 C. It held 4-year-old 

 brook and brown trout and adult landlocked salmon. A seine haul of fish were exam- 

 ined. Of 66 brook trout, 21.5 per cent had visible tumors and 19.5 per cent red floors; 

 of 15 salmon, i had a red floor and 4 had visible tumors; of 36 brown trout all were 

 entirely clean, without external sign of thyroid proliferation. The food was beef heart. 

 There was no marked mortality rate, but there was a heavy loss on spawn taken from 

 the fish of this pond. 



