CARCINOMA OF THE THYROID IN SAEMONOID 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, Caspar!, and Lohe (1912) and the results 
obtained by the use of colloidal metals by Szecsi (1912), 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 evidenee 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 
Salmonidae 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. 
