400 
BULLETIN OF THE BUREAU OF FISHERIES. 
the median line at the branchial junction and extends forward into the areolar tissue at 
the base of the tongue, and presents visible evidence of erosion of the large mass of carti- 
lage at the base of the tongue. The superior, anterior, and protruding posterior portions 
of this tumor are composed of a network of large alveoli, free from colloid, in which are 
embedded a number of dense nodular growths. One of these protrudes into the floor 
of the mouth, a group of larger ones forms the central portion of the tumor, and one or 
two small ones protrude into the anterior portion of the alveolar structure. 
Here we have plainly a distinct focal evidence of proliferation of a much more 
intense type than that involving the surrounding alveolar tissue growth. The small 
anterior nodule is found under high power to be composed almost exclusively (fig. 41) 
of closely packed spindle and oval cells with deeply staining nuclei in which the merest 
suggestion of an attempt at alveolar arrangement in some of the cell groups may be 
traced. In the distinct nodule lying in the floor of the mouth the alveolar structure 
is more apparent, and figure 42 shows a small, distinct nodule of adenomatous type. 
The margins of these more or less solid nodules in this tumor gradually merge into 
the loose alveolar structure forming the remainder of the tumor. In some tumors, 
however, we have found small nodules of closely packed alveoli, the cells of which stain 
deeply, with closely packed, deeply staining nuclei, the nodule embedded in a reticulum 
of more open alveolar structure, the cells of which are not in so active a state of prolifera- 
tion and do not stain so deeply. In many of these nodules expansive growth is evidenced 
by compression and displacement of the alveoli of the tumor tissue surrounding the 
nodule. (Fig. 43.) 
infiltration. 
In another aspect of the nodule one finds definite evidence of infiltration of sur- 
rounding thyroid tumor tissue by individual alveoli of the more malignant type. (Fig. 
44.) We have here definite evidence of infiltration of thyroid tissue by a nodule of malig- 
nant degeneration of more active type. The importance of this finding is that the 
infiltration in this instance does not deal with anatomical landmarks or adjacent struc- 
tures but represents a true infiltration, by a more malignant and rapidly growing portion 
of the thyroid tissue, of surrounding thyroid structure. 
A nodular development in the tumors indicates a more intense focal action of the 
stimulus causing these tumors. It has been suggested that proliferation of the thyroid 
in these growths in the Salmonidae is due to a reaction of the tissue to physiological 
demands. A marked characteristic of physiological hyperplasia is the uniformity with 
which the entire organ is affected. One of the most prominent characteristics of these 
growths in the thyroid in the Salmonidse is intensive local stimulation, which leads not 
only to nodules wnthin the tumor masses, but gives the visible growth a marked lobulated 
appearance. If these tumors represented a response to physiological demands, we 
should expect a more uniform character of the hyperplastic tissue. We should expect 
all of the thyroid tissue to be affected. In this connection the section of fish 158 is 
significant. Here we have an extensive tumor (diagram 45, p. 36) involving the entire 
region between the isthmus and the floor of the mouth, appearing at the branchial 
