CARCINOMA OP THE THYROID IN SALMONOID FISHES. 463 



aioi A. Small closely-packed follicles lined with flattened and low cubical epithelium. No colloid. Marked increase in 

 amount of thyroid tissue. Many follicles and flat strands of foUicles between the muscle bundles in the areolar tissue, floor of 

 the mouth, and bone cavities. Regression from well- developed hyperplasia. 



2103 A. About the large vessels are individual follicles lined with columnar epithelium, filled with faintly staining colloid. 

 These follicles are irregular in shape. Slight infoldings of the vesicular wall with beginning bud formation. Protoplasm of the 

 cells stains deeply. The nuclei are vesicular, of great variety of size. The long axes of the nuclei are perpendicular to the cir- 

 cumference. Marked hyperemia of the small vessels between these follicles. In the same field by low power may be seen 

 individual follicles of typical normal appearance, flattened epithchum filled with deeply stainable colloid. W'e have here 

 beginning focal hyperplasia. Certain groups of follicles are lined with flattened epithelium, contain no colloid, are elongate, 

 branching or irregular in shape, and present an appearance suggesting regression of individual follicles. 



2104 A, B. Marked increase of thyroid. Follicles closely packed and spherical, some filled with stainable colloid. Some 

 follicles of irregular shape or branching. Widely scattered follicles in the areolar tissue and between the fibers of the dense 

 connective tissue structures. Regression of hyperplasia. 



2111 A. Spherical and oval follicles filled with stainable colloid and lined with flattened epithelium. Engorgement of the 

 vessels between the follicles. Slight hyperemia. Normal. 



CHEMOTHERAPY.'^ 



THE EFFECT OF IODINE. MERCURY, AND ARSENIC UPON CARCINOMA OF THE THYROID. 



The knowledge of the occasional efifect of iodine as a remedy in goiter is almost as 

 old as our knowledge of the disease itself. The relation of iodine to the thyroid has 

 been the subject of extensive study by modem chemical methods and by biological 

 experiment. It is well known that the thyroid gland normally contains iodine, and it 

 has been contended that in certain hyperplasias of the thyroid the amount of iodine 

 per gram weight of thyroid tissue is reduced. These facts have led experimenters to 

 hold that the curative effects of iodine upon the hyperplastic thyroid is more due to a 

 restoration of the iodine content to a normal basis than to the specific action of iodine 

 administered as a remedy. In the mammalian hyperplastic thyroid there are fre- 

 quently encountered small adenomata which are more or less distinct in appearance from 



a The measures to be taken by fish culturists for the prevention of thyroid carcinoma must await a careful investigation planned 

 specifically with this end in view. This we have not been able to undertake. We believe, however, our experiments with 

 wild fish point the way along which efforts should be directed. 



The matter of food is undoubtedly the most important aspect of domestication in relation to thyroid disease. The livers of 

 cattle, sheep, and hogs are chiefly relied upon in rearing the salmonoids. and the extent to which this food is varied or replaced 

 by heart, lungs, horse flesh, and other animal proteids apparently docs not alter the situation in this respect. Their availability 

 as fish food makes it difficult to displace them, but fortunately they are not inherently necessary to fish culture. Vegetable food 

 made from staple grains, fresh-water and marine fish and mussels, Entomostraca and other Crustacea, live maggots and even 

 living adult insects, have been used more or less as foods in practical fish culture. Most of these are not yet available in quan- 

 tity, and none has displaced entirely the mammalian proteids. Our feeding experiments, however, indicate that such foods 

 ■would maintain normal thyroid glands in the salmonoid fishes. To devise and prove a composite ration properly balanced for 

 this purpose would seem a fish cultural problem worth while. Perhaps a cooked mixture consisting largely of vegetable 

 meal in which was incorporated fish flesh and a minor portion of one of the foods used commonly at present would promise 

 best. Possibly even small quantities of insects and insect larvte added to this would be an important improvement. Such a 

 food has ever been a prime desideratum in fish culture and affords a measure of protection against most fish diseases as well as 

 against the one now under discussion. 



Holding the disease to be an infection, the ultimate problem is largely one of prevention, under which would come a more 

 stringent cleanliness of fish troughs and ponds, possibly the annual painting of wooden containers and in the case of dirt ponds, 

 their occasional emptying with periods of sun-drying, or a change to cement construction. The selection and breeding of resistant 

 strains, or of resistant species like the Scotch sea trout, are obviously indicated. 



As for the presumption, which experiments indicate, of remedial possibilities in the use of mercury or iodine, there is no 

 sufficient basis at present for recommending their use on a practical scale. This would involve their administration over consid- 

 erable periods of time which their cumulative action might render undesirable. Moreover, that they are absolute preventives 

 of the disease process under discussion is not yet demonstrated. The control of this disease can doubtless be brought about by 

 other means than administration of chemical agents. To this end a fish-cultural station handUng preferably the brook trout 

 could well be devoted to the extended experiments having to do with feeding and the access of infection to the fish which are 

 necessary both to more exact knowledge of the disease and to its practical relations. 



