CARCINOMA OP TH6 THYROID IN SAI^MONOID PISHES. 409 



later that at least the first stages of this disease can be induced in mammals through the 

 drinking water, such a comparison at the present time becomes even more profitable 

 than formerly. The final relation of these tumors to tumors in mammals can now be left 

 to experimental investigation; especially the production in mammals of metastasizing 

 tumors would serve to clear up the possible relation between carcinoma of the thyroid 

 in the Salmonidae and carcinoma of the thyroid in mammals. For the present we con- 

 sider that we have more firmly established the fact already assumed by Plehn, Pick, 

 and many other investigators, that we are here dealing with carcinoma of the thyroid 

 in fish. 



Pick, in his excellent article, after having established the homotypic and hetero- 

 typic character of these tumors, compared them with the malignant epithelial tumors of 

 other animals, especially carcinoma of the breast in mice. This analogy of Pick's is well 

 taken and we feel that the progress of experimental cancer research has since demonstra- 

 ted many other points of analogy, which we shall deal with later. Pick also pointed out 

 that certain degenerative and regressive changes are common both to carcinoma of the 

 thyroid in fish and the epitheliomata of mammals. The impossibility of classifying 

 the different types of carcinoma of the thyroid in fish affords another point of similarity 

 with carcinoma of the breast in mice, where the greatest variety of histological appear- 

 ance may be found in the same tumor. A still closer analogy, according to Pick, is to 

 be found in the histological character of the growths of the thyroid in fish when compared 

 with similar tumors in man, although from the material at Pick's disposal he had no 

 evidence of metastasis formation, such as we are now able to bring. 



One of the most important contributions to our knowledge of the various types of 

 epithelial proliferation of the thyroid structure in man is found in a monograph, based 

 on very extensive material, entitled "On the Epithelial Forms of Malignant Struma, " 

 by Langhans (1907), in which this author classifies the various types of malignant 

 growths of the thyroid in man under the following heads : 



1. Proliferating struma. 



2. Carcinomatous struma, the usual irregular structure of carcinoma. 



3. Metastasizing struma. 



4. Para struma. 



5. Small alveolar, large-celled struma. 



6. Malignant papilloma. 



7. Squamous epithelioma. 



From a comparison of our material with that of Langhans we find that in the fish 

 tumors, areas of proliferation, or in some instances the greater part of the structure 

 of a tumor, may be said to conform to one of three of the six types described by Lang- 

 hans for man, namely, proliferating struma, carcinomatous struma, and malignant 

 papilloma. Figure 59 illustrates a tumor in which the preponderating type is almost 

 identical in appearance with the type described by Langhans for proliferating struma and 

 may be compared with figure 60, made at the same magnification from one of Prof. 



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