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 

 bv 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 Salmonidse 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 Salmonidae is intensive local stimulation, which leads not 

 only to nodules within 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 



