CARCINOMA OF THE THYROID IN SALMONOID FISHES. 381 



fish. The examination of specimens of the offspring of the older fish at the fingerling 

 stage reveals the thyroid of occasional specimens in a state of simple hyperplasia (fig. 

 20), perhaps slightly more marked than that found in the wild fish from Algonquin 

 Park. (P. 75.) 



In these small fish the thyroid is not markedly increased in amount and is largely 

 localized about the great vessels, but occasional groups of alveoli are found somewhat 

 more widely removed from these structures than normal, and occasional small groups in 

 the infoldings of the cartilage or bone or between the muscle bundles. The alveoli are 

 not unusually large, the epithelium is high cuboidal and low columnar, the long axes of 

 the nuclei perpendicular to the circumference of the alveoli. Both protoplasm and 

 nucleus stain more deeply than normal. The colloid is diminished in amount and stains 

 less well than in the normal specimens. (See fig. 20, which may be compared with 

 a similar photograph at the same magnification of a Scotch sea trout from the same lot, 

 2050 A, fig. 19, in which the thyroid structure presents a characteristic normal appear- 

 ance, and both may be compared with a fish of similar size taken in the wild state from 

 the Au Sable River, Mich., fish 199 A, fig. 19, of which an illustration at similar magni- 

 fication is provided.) The thyroid gland of the adult Scotch sea trout, when viewed in 

 the light of the conditions found in the smaller fish, in which occasional examples show 

 simple hyperplasia and the larger proportion strictly normal thyroid tissue, reveals a 

 similar division in character of the thyroid in the adults. A larger proportion of the 

 adult Scotch sea trout presents strictly normal thyroid tissue. (Fig. 21.) There does 

 not appear to be an increased amount of thyroid for the size and age of these fish. The 

 minority of the fish, however, presents microscopically a condition of the thyroid which 

 may be spoken of as colloid goiter. (Fig. 22.) In them the alveoli are greatly increased 

 in size, the total amount of thyroid is also increased, the walls of the alveoli are very 

 thin, the epithelium pressed very flat, and the lumina compactly filled out with large 

 masses of colloid. 



From a careful study of the Scotch sea trout, it is clear that although, as will be 

 shown later, they are almost perfectly immune to carcinoma of the thyroid, a certain 

 proportion of them are affected by a process of simple hyperplasia which terminates 

 by resolution in colloid goiter. It will be shown later that spontaneous recovery of 

 carcinoma of the thyroid in the Salmonidae produces an entirely different terminal 

 picture from that of colloid goiter. In the instance above described of the Scotch sea 

 trout, the transformation of hyperplasia into colloid goiter has been brought about by 

 a process which has been termed resolution. In carcinoma the disappearance of the 

 tumors in spontaneous recovery is brought about by a process of regression, a part of 

 which may be referred to as resolution; that is, the epithelium undergoes changes of 

 type, colloid reappears, but the bulk of the tumor literally retrogrades. Many of the 

 alveoli totally disappear and large areas are frequently removed so rapidly as to require 

 extensive repair by connective tissue. All of the characteristic appearances found in 

 regression of malignant mammalian tumors, such as the frequency of large areas of hem- 

 orrhage followed by repair, the formation of pseudogiant cells by coalescence of the 

 epithelium, great increase in the connective tissue stroma especially at the margins of 



