458 BULLETIN OF THE BUREAU OF FISHERIES. 



increase in the number of thyroid follicles without elevation of epithelium or other 

 changes from the normal. Lot 2163 was exceptional in that two of three fish showed 

 beginning hyperplasia. They had been inoculated with trout tumor material in the 

 thyroid region, the implant failing to take. 



At the examination of June, 1912, two years after the beginning of the experiment, 

 one distinct thyroid tumor (fig. 90) had developed in lot 2146 under the feeding of raw 

 heart muscle. This fish, and one lot 2147, which was fed raw liver and had developed 

 a red floor, with slight swelling, showed typical thyroid carcinoma. Of the rest many 

 had developed red floors, as shown in table viii. One or more specimens were preserved 

 from each lot, and a description of the histology of the thyroid is given below. The 

 trout fed with marine fish, vegetable, and natural food still remained normal, while carci- 

 noma has definitely developed in two of the sample fish fed raw animal food. Those fed 

 cooked liver have passed through hyperplasia to regression and, in fact, the chief char- 

 acteristic of the microscopic picture in all the fish on meat diet is the regression indi- 

 cative of spontaneous recovery. (Fig. 91-92.) 



In general, it may be stated that the results obtained by selected feeding are in 

 accord with our experiences in the study of hatchery conditions and that the relation 

 of foodstuffs to the incidence of the disease is contributory and not causative. Thus 

 raw liver and raw ox heart used as a food act as a predisposing factor in the develop- 

 ment of carcinoma of the thyroid. Cooking the same food tends to delay the advent 

 of the disease and fish fed upon natural food, marine fish, and vegetable food are able 

 to resist the disease for a considerable period of time, if not indefinitely. One might 

 conclude from these experiments that raw liver and raw heart muscle were the sole 

 cause of the disease, were it not for the fact that we are able to check this observation 

 by an observation made at another hatchery where the conditions are practically 

 reversed. In this hatchery all of the fish are fed upon raw liver and raw ox heart muscle ; 

 but the fish kept in one water supply are free from the disease with this type of feeding, 

 whereas those kept in other tanks with a slightly different water supply are uniformly 

 affected by the disease. This state of affairs exists at Cold Spring Harbor, N. Y. The 

 hatchery building is supplied with water from an artesian pipe driven near the building. 

 The overflow from the hatchery, and, of course, from the artesian supply, which is not 

 required for the hatchery building, flow into a series of large earth ponds, and then 

 a series of concrete-lined ponds. The arrangement of the concrete ponds is such that 

 one pond is practically continuous, each division for fish being separated from the one 

 above it by an arrangement of boards over which the water flows. The ponds and 

 concrete tanks are old and at the time of examination were lined with a visible growth 

 of green algae. 



Young fish hatched in the hatchery in the artesian water were placed for the most 

 part in the concrete tanks just mentioned, but in a few instances the lots were di\dded 

 and approximately half were placed in a spring located a distance of several hundred 

 yards from the hatchery building. This spring flowed out from a hillside obviously 

 from the same general supply as the artesian water and the springs near the hatchery. 



