4o6 
bulletin of The bureau of fisheries. 
The tumor is of alveolo-tubular type, the greater proportion of it solid. It involves 
the muscularis mucosa of the intestinal wall, bundles of muscles derived from this struc- 
ture running through its substance. In the more open portions of the tumor, alveoli 
containing colloid may be found. Under higher power (fig. 57) the epithelium of the 
tumor both in the alveolar and tubular types consists of large cells generally of high 
columnar type. The protoplasm is deeply stained; the nuclei are vesicular, of basilar 
location. In some areas marked variation in size and character of the epithelial cells 
is evident. Karyokinetic figures are not infrequent. The heterotypic nature of the 
epithelial cells is best seen in the region where the muscular coat of the intestinal wall 
is infiltrated. (Fig. 57.) 
The larger proportion of the tumor is rather regular in formation, homotypic in 
character. In many places the epithelium is so closely packed that scarcely any evidence 
of alveolar structure may be made out. The relation of the intestinal lumen to the 
tumor growth is of peculiar importance. Carefully scanning the tumor under low power 
a point may be found where the intestinal epithelium spreads out into a single layer 
upon the surface of the tumor. (Fig. 55.) There is no evidence of transition from the 
intestinal epithelium into that of the tumor; in fact the marked columnar character 
of the intestinal epithelium, with its frequent goblet cells, is clearly distinguished against 
the background of tumor tissue. Upon the surface of the tumor the single layer of 
epithelium from the intestinal papillae extends for a considerable distance upon the sur- 
face of the tumor, the uppermost portion of which is, however, eroded. Evidences 
of occasional hemorrhages upon the surface may be found, the apex of the tumor being 
covered with a distinct clot. In other portions of the tumor the characteristic appear- 
ance of alveoli of irregular shape generally filled with colloid is to be found and in this 
region the tendency to papillary growths within the alveoli is quite distinct. (Fig. 
56.) In this region also the structure of the muscularis mucosa is apparent, and the 
marked infiltrative character of the tumor is here distinctly evident. 
The histologic diagnosis of this tumor is to our mind quite clear. It consists of 
thyroid tissue presenting the characteristics of the alveolo-tubular type of tumor of the 
thyroid in the Salmonid^. It furthermore presents in certain areas that tendeney to 
papillary formation which is so frequent in these tumors. The histological picture 
and the presence of colloid quite clearly determine the nature of this growth. It is 
greatly to be regretted that through an unforeseen accident the thyroid region of this 
fish was not preserved. We have no evidence as to the nature of the primary growth 
in the thyroid region. Although the fish presented no macroscopic evidence of tumor, 
yet there is little doubt that a primary tumor in the thyroid region existed. The fish 
was taken from a hatchery in which one of the most outspoken epidemics of the disease 
we have yet encountered was in full progress. As all of the brook trout of this age 
succumbed to the disease in the course of two seasons, and as every specimen taken 
from the pond in which this fish was found presented macroscopic or microscopic evidence 
of the disease, there is little reason to doubt that we have here to deal with a metastasis 
from a tumor originating in the thyroid tissue of this fish. 
