CARCINOMA OF THF THYROID IN SADMONOID FISHES. 
397 
From their position they are subject to mechanical erosion on their ventral surface. 
When well developed the tumor usually fills and completely obliterates the pit. When 
the latter is not the seat of tumor growth, it is sometimes completely everted by the 
pressure of the tumor from the main thyroid region, and almost all trace of it lost, the 
surface of the skin being stretched smooth in this region. 
Table I. — Classification of Visible Tumors by Location. 
Visible tumor presenting at — 
Number. 
Visible tumor presenting at — 
Number. 
pit 
5 
Branchial junction: 
6 
Branchial junction, gill region, pit, floor 
6 
6 
27 
visible tumors examined 91 
HISTOLOGY. 
EARLY STAGE. 
Under “Simple Hyperplasia” we have presented evidence which we believe indicates 
that there occurs in wild and domesticated fish a type of simple hyperplasia which leads 
to colloid goiter. The first changes in the epithelium in any form of hyperplasia, 
whether simple or malignant, would be of the same character and thus indistinguishable 
one from the other. The progress of carcinoma of the thyroid in the Salmonidae may 
for convenience be divided into three periods : That in which only microscopic evidence 
of hyperplasia is discernible ; the stage in which the growth of tissue extends sufficiently 
to produce hypersemic changes visible in the floor of the mouth — i. e., red floor; and then 
the period of visible tumors. Histologically no line of demarcation is possible between 
these various stages. Neither is it possible to distinguish the very first changes in the 
epithelium at the onset of this disease from simple hyperplasia leading to colloid goiter 
as we have observed it in the Scotch sea trout which have proven immune to carcinoma 
of the thyroid. 
Normal thyroid tissue in the Salmonidse is composed of isolated follicles lined with 
flattened epithelium containing colloid. The follicles are distributed as shown about 
the aorta in the loose connective tissue. 
The first indication of the disease is found in the hypertrophy of individual cells; 
in a given follicle usually the change affects one or two adjacent follicles, or the only 
evidence of the beginning of the disease is found in a small group of follicles lined with 
cubical or columnar epithelium in which the colloid is greatly reduced or entirely absent. 
Hyperemia of the vessels of the stroma is usually present. In our experiments with 
wild Wisconsin brook trout, in which fish of varying size and age were taken from the 
wilderness and placed in the waters of the Craig Brook hatchery, the first evidence of 
60289°— Bull. 32 — 14 26 
