CARCINOMA OF THE THYROID IN SAEMONOID 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 circu mf erence 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 alveoh 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 
60289° — Bull. 32 — 14 25 
