CARCINOMA OF THE THYROID IN SALMONOID FISHES. 469 



day, and in one instance where a fish with a large tumor (fish 1 136 of table xii, fig. 108) 

 was subjected to mercury by immersion for three and one-half hours in water containing 

 a much higher concentration than usual, by which it was apparently poisoned and 

 promptly died, the changes in the tumor were comparable to results obtained only 

 by an exhibition of mercury at i : 5,000,000 during a period of not less than 20 days. 



Since the experiments above referred to were completed, our knowledge of the action 

 of the heavy metals upon carcinoma in experimental animals has been amplified by the 

 experiments of von Wassermann, who has shown that the intravenous injection of 

 selenium in combination with eosin, when given in large doses, is capable of causing the 

 complete regression of large implanted mouse cancers, followed by clinical cure. In 

 considering the results obtained by ourselves in carcinoma of the thyroid in the Sal- 

 monidse, showing the pronounced effect of iodine, arsenic, and mercury, it became 

 evident to us, after the publication of von Wassermann's results obtained with selenium, 

 that it was highly probable that suitable compounds of any of the heavy metals would 

 prove to have a more or less distinctive effect upon neoplasms. That this is the case 

 is now shown by the publication of Neuberg, Caspari, and Lohe (1912) and the results 

 obtained by the use of colloidal metals by Szecsi (191 2), and the favorable, although 

 temporary results obtained by the French observers in the use of colloidal copper in 

 human carcinoma. 



All of these experiments, as did the original observations of Schoene, dealt with 

 large doses, in many instances almost a fatal dose of these metallic compounds given 

 intravenously. Lewin (1913) has recently pointed out that where immediate results 

 are obtained with metals, there is evidence of marked hemorrhage into the tumor, and 

 believes that they are able to affect the tumor by their ability to injure the capillary 

 terminals, this explaining the hemorrhage. Although in our experiments arsenic and 

 mercury were used in very great dilution, we have the same evidence of hemorrhage 

 into the tumors, especially the large ones that are obtained by injecting much larger 

 doses intravenously in animals. It seems highly probable that the results obtained 

 with this great dilution are due to a cumulative action of the metal. It is, however, 

 clear that the results obtained in our experiments are of the same nature as those 

 obtained in neoplasms of experimental animals by intravenous injection. (Gaylord, 

 1912 a.) 



It seems assured that the action of iodine upon the tumors of the thyroid in the 

 Salmonidse is not due to its physiological relation to the thyroid gland; that its curative 

 qualities are equally possessed by other elements, including the heavy metals, and that 

 it acts by virtue of some quality which it shares in common with the metals; that these 

 metals exhibit the same effect upon true neoplasms in mammals and that the effect of 

 iodine and metals upon the tumors of the thyroid in the Salmonidae tends to prove their 

 true neoplastic nature, and that the theory of Marine and Lenhart that the action of 

 iodine may be used to distinguish between physiological hyperplasia and true tumor 

 formation is untenable. 



