502 BULLETIN OF THE BUREAU OF FISHERIES. 



are not present. In the second control puppy, no. 20, they are present. It is this 

 control, no. 20, which is described as having slight evidence of hyperplasia, but as this 

 dog received before the beginning of the final experiment, as did also the other controls, 

 water from pond 10, it is possible that it acquired the worms at that time. The mother 

 dog, no. 19, and the other control puppy, no. 22, also received pond 10 water and 

 showed no evidence of hyperplasia or nematodes. 



There is apparently no direct connection between the hyperplasia of the thyroid 

 and the nematodes. As previously described, the hyperplasia of the thyroid in these 

 experimental animals is diffuse. If the nematodes have any direct relation to the experi- 

 mental hyperplasia of the thyroid thus produced, it is only as a carrier of the virus of the 

 disease in the manner which Borrel has suggested for tumors in mammals. That hyper- 

 plasia can result without nematodes or other possible carriers is shown by the fact that 

 we have not found anything of the sort in the hyperplasia of the thyroid in the rats, 

 induced with water and scrapings from Craig Brook. Bircher or the other authors 

 who have produced experimental goiter in animals have not noted the presence of nema- 

 todes. Nematodes in the region of the thyroid in fish are certainly not necessary to 

 the development of the disease in fish. We have in one or two instances found similar 

 tubercles usually lying in the subcutaneous tissue below the floor of the mouth in which 

 coiled-up nematode remains have been found. A portion of the cuticle of such a nema- 

 tode was sufficiently preserved so that its structure could be clearly made out. (Fig. 126.} 

 There is evidence in the dog thyroids that some of the nematodes perish. The finding 

 of disintegrating tubercles is subject to this interpretation. (Fig. 125.) It is therefore 

 possible that in the very early stages of the transmission of the disease it will be found 

 that such nematodes act as occasional carriers in this affection and that later they 

 disappear. A careful study of the intestinal contents of the fish and the scrapings 

 from the fish troughs will be included in the next stage of this investigation. 



SUMMARY. 



I. The present investigation of thyroid carcinoma among fish was begun by the 

 Director of the Gratwick Laboratory in furtherance of the inquiry of that institution 

 into the nature of cancer in man. Having brought it to the attention of the United 

 States Bureau of Fisheries through the President of the United States, an investigation 

 of wider scope resulted, based upon its interest and importance to fish culture and to 

 cancer research in general, and uniting the Federal and State resources as represented 

 by the Bureau and the Gratwick Laboratory. 



Bonnet in 1883 described a gill disease in trout which is undoubtedly identical with 

 the subject of this inquiry, and is thus the first published reference to it, though the 

 nature of the disease was not at that time recognized. Scott in 1891 first identified the 

 disease as carcinoma, without recognizing its relation to the thyroid gland. Its origin 

 in the thyroid was first asserted by Plehn in 1902, who diagnosed it as adeno-carcinoma. 

 Pick in 1905 published the first extended study of the structure of the growths and 

 insisted on their carcinomatous nature. Gillruth in 1902 described it briefly as an 



