CARCINOMA OF THE THYROID IN SALMONOID FISHES. 407 



We have expressed our reason for holding that the growths on the apex of the 

 jaw and this growth in the wall of the intestinal tract just within the anus are instances 

 of genuine metastasis formation. We believe that a wider understanding of the natural 

 history of carcinoma of the thyroid of the Salmonidae will show that a case described 

 by Marine and Lenhart (1911a, p. 470) is more probably a metastasis than a tumor 

 springing from misplaced thyroid. These authors describe an abdominal goiter in a 

 29-months-old fish. The thyroid mass was round, circumscribed, and measured one by 

 one-half cubic centimeter, was attached to the cardiac end of the stomach by a connective 

 tissue pedicle and extended into the abdominal cavity. The fish had a large ventral 

 tumor histologically identical with the abdominal growth. Because an examination 

 of the xdsceral regions showed no such deposits of thyroid tissue, these authors looked 

 upon this specimen as an enlarged aberrant thyroid deposit. They also report having 

 seen growths on the tip of the lower jaw in from 2 to 3 per cent of all fish with visible 

 tumors examined by them, and these they also hold to have sprung from misplaced 

 thyroid deposits. 



COMPARATIVE PATHOLOGY. 



The study of hyperplasia and carcinoma of the thyroid in the Salmonidae, on account 

 of the great similarity in the changes in the organ of the fish to that occurring in mam- 

 mals, seems likely to throw important light upon the origin of certain structures which 

 have been the subject of extensive study in the thyroid of mammals. Virchow (1863), 

 Wolfler (1883), Hitzig (1894), and Michaud (1906) have described in the thyroid of 

 man small adenomata, the condition being known as struma nodosa. Virchow held 

 that these nodules developed by proliferation from the follicles of the thyroid. Wolfler 

 held that they developed from misplaced embryonic rests. Hitzig evidently opposed 

 the theory of Wolfler as to the embryonic origin of these nodules and held that they 

 developed bv proliferation from the normal tissue of the thyroid, for the reason that 

 in normal thyroids they were never found. Michaud has carefully studied the genesis 

 of these adenomata and agrees with Virchow and Hitzig that they are formed by pro- 

 liferation from normal structures of the thyroid. 



According to Michaud these growths develop by changes in the epithelium of 

 normal follicles, which take on columnar type and through proliferation of the cells form 

 extensions and protrusion of the follicles and finally by budding produce new follicles 

 which become detached from the original. The first changes, which are focal, are 

 restricted by the surrounding stroma, which takes no part in the change. From this 

 point on the nodule grows by proliferation of the structures within it, especially those 

 toward the center. The very first evidence of this change is found by Michaud in the 

 presence in the thyroid structure of long, tortuous clefts or tubes with cubical or colum- 

 nar epithelium, staining more deeply than the surrounding structures, these tubules 

 having already been noted and described by Hitzig. From these tubules, by the process 

 of budding above described, are developed focal nodules, i. e., struma nodosa. 



It will be seen that the description given by Hitzig and Michaud for the development 

 of these isolated adenomata in the mammalian thyroid is exactly like the beginning 



