CARCINOMA OF THE THYROID IN SALMONOID FISHES. 455 



tember i, 1909, and killed for examination November 24, 1909, showed at the point of 

 inoculation, which was in the muscular structure of the abdominal wall, just anterior to 

 the left ventral fin, evidence of a small protruding growth the size of a grain of rice. On 

 sectioning this tissue, a slender growth is found extending in what must have been the 

 track of the needle. Under the microscope the growth is made up of a series of nodules, 

 most of them with a not very well-defined connective tissue capsule. The continuity 

 of the epidermis at the point of the small tumor is broken, and we have here a growth of 

 tissue connected with the nodular growths in the deeper structures. This protrudes 

 through the broken continuity of the epidermis. The circumscribed nodules lying be- 

 tween the muscle bundles and the subcutaneous tissue are made up of large spindle 

 and irregularly shaped cells. The centers of the larger nodules contain a certain amount 

 of hyaline detritus. Scattered between the cells of the nodules, particularly toward the 

 center, are many leucocytes. At the outer margins of the nodules the cells are best 

 preserved. The nuclei vary greatly in size, the protoplasm stains, the cell boundaries 

 are not always well defined. The growth is made up of a complex of cells with large 

 vesicular nuclei containing one or more nucleoli. They may be recognized as thyroid epi- 

 thelium. In a nodule which fills the break in continuity in the epidermis there is a dis- 

 tinct suggestion of tubular arrangement with a definite stroma carrying blood vessels, 

 and at the margin of one or two of the other nodules definite alveoli may be made out. 



Toward the centers of the nodules there is distinct evidence of atrophy of the cells, 

 associated with clumps of chromatin and hyaline detritus. There are many cells with 

 very large nuclei. There is generally a great difference in the size and shape of the 

 nuclei. Rarely a karyokinetic figure is found. The cells are closely packed together, 

 but in some nodules there has evidently been a growth of capillaries in attempts at forma- 

 tion of a stroma. From the microscopic picture it is evident that there has been some 

 proliferation in the implanted tissue, and that three months after portions of the graft 

 at least are still alive. 



At Craig Brook station in 1910 implants were made directly into the thyroid region 

 of the fish with the aid of a hypodermic needle. It was found that the trout will endure 

 a needle puncture in the floor of the mouth and the injection of one-fifth cubic centimeter 

 of physiological salt solution directly into the tissues containing the thyroid with little 

 reaction. By inserting the needle a little to one side of the median line the ventral 

 aorta is avoided, and most of them show no external bleeding. Some of the fish suffer 

 from shock, due to the puncture, from which they recover within 5 to 20 seconds. Even 

 those which bleed usually do not succumb. Of 76 yearling domesticated trout thus 

 inoculated as controls, only i died as a result of the manipulation. The fish tumor 

 material for inoculation was groimd up and mixed with its own volume of physiological 

 salt solution. The difficulty in planting this material in the tissues of the trout lies in 

 the high toxicity of the tumor extract. It is not practicable to place transplants of 

 ordinary size in this vascular region without heavy loss from toxemia. The tumor 

 material varies considerably in toxicity. Domesticated trout endure the mechanical 

 injury incidental to inoculation better than wild trout. 



