CARCINOMA OF THE) THYROID IN SALMONOID FISHES. 
399 
visible tumor stage — structural types. 
In the larger tumors one finds a remarkable variation in the histologic picture. 
The fundamental types may be divided into four — alveolar, papillar, tubular, and solid. 
In occasional tumors one of these three types definitely predominates. In the lOO 
tumors selected for study these types occur in the following proportions; 
Types. 
Per cent. 
Fig. No. 
38 
One is struck, however, in the study of these large infiltrating tumors, with the 
remarkable variety of formation to be found in various regions. One may find in a 
single tumor areas which may be placed under any one of the designations given. The 
action of the stimulus upon the thyroid tissue in these tumors appears not only to work 
irregularly, as will be shown by the advent of nodules of active proliferation and areas 
simulating hyperplasia, but appears to throw the entire thyroid tissue into such a riot 
of proliferation that a definite type for the entire tumor is seldom accomplished. The 
epithelial cells forming the tumor present the greatest possible variety of form and size. 
The nuclei are usually vesicular, in entire areas of a tumor the cells may present a typical 
spindle form, thus simulating sarcoma, and in some instances areas of the tumor are 
made up of a background of spindle cell tissue, through which are scattered small but 
definite alveoli containing colloid. (Tig. 38.) 
In such a tumor we have a picture analogous to the so-called mixed tumor of the 
thyroid encountered in man. Occasionally tumors may be met in which a large propor- 
tion of the tumor is made up of large alveoli packed with solid masses of large cells, 
deeply staining protoplasm and vesicular nuclei, and frequent karyokinetic figures, pre- 
senting the picture of proliferating struma. (Langhans.) (Fig. 39.) 
Again, the general predominating type of a tumor may be distinctly papillary, in 
which large vegetations covered with columnar epithelium and deeply stained nuclei 
are found projecting into irregular spaces, usually free from colloid. The tendency 
to papillary formation may be found in almost all of these tumors. Occasionally these 
papilliform areas are of nodular form, in which case the cells forming the papillary nodule 
are more deeply stained than the surrounding tubular or alveolar type, which gives 
them a distinct focal character. (Fig. 45.) This marked tendency to focal or nodular 
development within the tumors occasionally produces growths in which we have a large 
mass of tubulo-alveolar structure, with nodules of solid, closely packed areas of intensive 
proliferation. In figure 40 we have a low-power picture of such a tumor. The tumor 
mass involves the entire area between the base of the tongue and the pericardial space and 
extends between the arches to the floor of the mouth, where it projects in a series of 
large protrusions, has pushed down the muscular structure of the isthmus, protrudes in 
