504 BULLETIN OF THE BUREAU OP FISHERIES. 



reached a sufficient amount to produce the red-floor stage. Bone, cartilage, and muscle 

 are invaded. The growth no longer seeks the paths of least resistance. 



In the visible tumor stage there is a remarkable variation in the character of the 

 proliferation. All the various types occur in one tumor. They may be divided into 

 alveolar, tubular, and solid, and combined with papillary and cystic types. Frequently 

 small adenomatous structures of malignant appearance are found grading and infil- 

 trating the surrounding thyroid structure of less malignant appearance. Occasionally 

 islands of normal thyroid tissue have been found in the bone spaces or cavities of the 

 bone where the entire surrounding structure was replaced by thyroid carcinoma. True 

 infiltration of bone, cartilage, vessel wall, muscle, and skin has been demonstrated. 

 Occasionally tumors are met with which present the appearance of so-called sarco- 

 carcinoma of the thyroid in mammals; a background of spindle cells resembling sarcoma 

 with occasional alveoli. 



Growths upon the apex of the lower jaw are either implantations or metastases. 

 A marked similarity of the primary tumor in the thyroid region with the growth upon 

 the tip of the jaw in one case studied indicates that this is probably metastasis formation 

 at the site of an injury. An undoubted case of metastasis formation is found in a tumor 

 growing in the intestinal wall at the lower end of the intestinal tract, which infiltrated 

 the muscularis mucosa of the intestinal wall, of characteristic thyroid carcinoma struc- 

 ture, large irregular follicles lined with columnar epithelium, occasionally containing 

 colloid. Portions of the tumor present an appearance closely approximating the least 

 malignant appearing primary tumors. The character of this growth and the region in 

 which it occurred shows conclusively that it is a metastasis. 



A comparison of the various types of thyroid carcinoma of the Salmonidge shows 

 that they approximate in type three of the groups made by Langhans for carcinoma of 

 the thyroid in mammals, viz, proliferating struma, carcinomatous struma, and malignant 

 papilloma. 



V. Three examples of the disease have been found in wild fish in the United States. 

 One occurred in a brook trout which may have been planted from a hatchery, one in 

 a landlocked salmon, and one in a whitefish. None of the species of whitefishes is fed 

 or reared artificially. 



VI. The disease has been observed in 16 species of salmonoids, or in hybrids made 

 among these. 



The geological formation at the sources of the water supplies in which the disease 

 occurs has apparently nothing to do with its origin, nor has the dissolved content of 

 the water. 



The disease is usually endemic and occasionally epidemic. It occurs in ponds and 

 troughs, of whatever construction, in which fish are held, reared, and fed the ordinary 

 proteid foods of fish culture, viz, raw liver, heart, lungs, and other meats. It shows a 

 tendency to increase from above downward in the course of a given water flow. Hybrids 

 of the Pacific salmon are especially susceptible and show a high incidence. When 

 endemic, the course of the disease is slow and chronic, with a low death rate made 

 indeterminate by complication with intercurrent or terminal infection and other 

 causes of death. The incidence of tumors varies greatly and increases with the age of 



