when it is seen that the disease is not exclusively among trout and salmon nor only among the subjects of fish culture. An adult whitefish was taken during the past winter from Lake Keuka, N. Y., with a well developed thyroid tumor. There has recently come to light a museum specimen of an adult brook trout caught in 1902 in Hosmer's Creek, a stocked stream in western New York, having a large thyroid tumor. This was to all intents and purposes a wild trout, though it may have been derived from a domesticated fish. The whitefish, however, are not artificially fed in hatcheries and are held scarcely beyond the hatching period. The causative factors of the disease which are intensified in the artificial fish ponds are present also among the natural conditions surrounding wild fish. The prevalence of the disease among salmonoids has doubtless to do with the great extent to which these fish are cultivated as well as with a natural susceptibility to thyroid enlargement. The disease runs usually a slow chronic course, with occasional acute outbreaks of more rapid progress and higher death rate. Ordinarily only a low mortality accompanies it but it is difficult to say just what this is, since secondary causes are probably the immediate cause of death of many tumor fish. There is no definite picture of symptoms and effects of tumor growth upon the fish. The mere mechanical effect of the growth by interfering with breathing and eating is certainly considerable but does not explain all the cases of marked anemia and poor condition, reaching sometimes to extreme emaciation. The material of which the tumor is composed contains some substance, probably identical or similar to the extract of the thyroid gland, which is highly toxic to the fish when injected into the circulation. When the tumor is ground up, mixed with one to three volumes of physiological salt solution, and about 1/10 c.c. of this injected directly into the thyroid region many of the fish are killed, in some cases nearly everyone injected. This fact interferes greatly with efforts to trans plant the tumor from fish to fish. Both the fluid extract and the undiluted particles of tumor are alike fatal. Thus every fish bearing even a small visible tumor is carrying on its own body many times a fatal dose of poison, which is harmless only because it is withheld from the circulation. The beginning of enlargement occurs in the hatchery during the first few months of the existence of the fish and practically all individuals are affected. The external appearance is perfectly normal. The visible tumor stage is usually not reached until the fish become yearlings. One brook trout of five months, however, was found dead with an advanced type of thyroid disease. Among the yearlings the tumor is seen upon handling and examination, and they may have tumors of relatively large size. In the older fish the enlargement reaches its greatest development. The percentage of fish bearing visible tumors varies greatly. Four per cent has been observed among brook trout yearlings, and 30 per cent among older ones and these are probably not extraordinary cases for this species. In acute outbreaks nearly every fish may show tumors. Hybrids of certain of the Pacific salmon, as the blueback and humpback, in process of rearing seem to be especially susceptible and the disease runs through them like an epidemic. In one case 16 per cent of visible tumors in April increased to 92 per cent by the following August, with an accompanying heavy mortality. Humpback salmon yearlings in fresh water at a hatchery showed the same involvement and rapid course. If we add to those showing visible tumors the number showing the red floor only we get a substantial increase, the total indicating the number showing some visible evidence of thyroid enlargement. Brook trout adults frequently have half the fish or more in this category. The effect of the tumor is obviously in part mechanical. It is difficult to separate the effect of mechanical interference with respiration and feeding from the systemic or constitutional effect of an internal secretion capable of bringing about the same anemia and inanition that follows such interference. There is certainly an anemia, sometimes very marked, in fish with the tumors but it is not an invariable accompaniment. Moreover, this anemic condition is not well correlated with the size of tumor and amount of mechanical interference, the extreme anemias sometimes occurring with the smallest tumors and the high blood readings with large tumors. Of ten two-year old brook trout with tumors of various sizes the hemoglobin readings averaged 16.9, with 29 for the highest and below 10 for the lowest, the limit for the instrument used. The average of 8 healthy, clean fish of the same lot was 37, with none under 30. This very clearly and definitely shows a paler blood accompanying the tumors and it is not improbable that the tumor has a physiological effect in many instances. The thyroid gland being normally almost microscopic, and in its enlargement reaching beyond the size of a walnut, must proliferate enormously. In doing so its structure passes through a wide range of changes and presents very diverse pictures, not only in different tumors but in different parts of the same tumor at one time. These pictures are typically those of goiter and cancer. We have to do with a process which is anatomically continuous, that is. the tumor or enlargement is an anatomical entity from its earliest increase to the largest growth or most advanced stages, whatever phases it passes through. This is less true of the nature of the pathological process. At the beginning it is a fish goiter, or is analogous to goiter in man. At the end it is fish cancer or is analogous to thyroid cancer in In both man and fish thyroid cancer begins as a goitrous enlargement, and there is the same difficulty of a dividing line in both. We have to do with a border line process which is pathologically various, which naturally leads to and includes cancer, without a sharp line of demarcation. Every tumor cannot be placed definitely in its entirety in one or the other category. The diagnosis of incipient goiter in fish is simple, while that of thyroid cancer in fish is complicated by a lack of absolute standards. The |