American Fisheries Society 383 



such interference. There is certainly an anemia, sometimes 

 very marked, in fish with the tumors but it is not an in- 

 variable accompaniment. Moreover, this anemic condition 

 is not well correlated with the size of tumor and amount 

 of mechanical interference, the extreme anemias sometimes 

 occurring with the smallest tumors and the high blood 

 readings with large tumors. Of ten two-year old brook 

 trout with tumors of various sizes the hemoglobin readings 

 averaged 16.9, with 29 for the highest and below 10 for the 

 lowest, the limit for the instrument used. The average of 

 8 healthy, clean fish of the same lot was 37, with none 

 under 30. This very clearly and definitely shows a paler 

 blood accompanying the tumors and it is not improbable 

 that the tumor has a physiological effect in many instances. 

 The thyroid gland being normally almost microscopic, 

 and in its enlargement reaching beyond the size of a walnut, 

 must proliferate enormously. In doing so its structure 

 passes through a wide range of changes and presents very 

 diverse pictures, not only in different tumors but in dif- 

 ferent parts of the same tumor at one time. These pictures 

 are typically those of goiter and cancer. We have to do 

 with a process which is anatomically continuous, that is. 

 the tumor or enlargement is an anatomical entity from its 

 earliest increase to the largest growth or most advanced 

 stages, whatever phases it passes through. This is less true 

 of the nature of the pathological process. At the beginning 

 it is a fish goiter, or is analogous to goiter in man. At the 

 end it is fish cancer or is analogous to thyroid cancer in 

 man. In both man and fish thyroid cancer begins as a 

 goitrous enlargement, and there is the same difficulty of a 

 dividing line in both. We liave to do with a border line 

 process which is pathologically various, which naturally 

 leads to and includes cancer, without a sharp line of demar- 

 cation. Every tumor cannot be placed definitely in its 

 entirety in one or the other category. The diagnosis of 

 incipient goiter in fish is simple, while that of thyroid cancer 

 in fish is complicated by a lack of absolute standards. The 



