504 
BUI^IvETlN OF THE BUREAU OF 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 ^nji^ading 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 Salmonidae 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 i6 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 
