464 BULLETIN OF THE BUREAU OF FISHERIES. 



the surrounding hyperplastic tissue and have been looked upon as developing from 

 embryonic rests, especially rests of. the original tubular structure of the fetal gland. 

 From these adenomata the malignant neoplasms of the thyroid are supposed to take 

 their origin. 



Marine and Lenhart (igiob, p. 20; 191 la, p. 22), who have extensively studied the 

 effect of iodine upon the mammalian thyroid, have advanced the theory that hyperplasias 

 of the thyroid including endemic goiter are due to insufficiency of iodine in the diet of 

 the individuals and that the therapeutic effects of iodine are the result of restoring to 

 the thyroid the normal amount of iodine. They state that nodular struma or the ade- 

 nomas found in strumous thyroids are unaffected by iodine, and that malignant tumors are 

 unaffected by iodine, and they propose that the administration of iodine shall constitute 

 a biological test for the purpose of distinguishing between hyperplasias which they hold 

 to be due to a physiological deficiency of iodine and malignant tumors which they state 

 can not be affected in this way. The evidence of the microscope is no longer to be con- 

 sidered; the final test is to be whether or not a given enlargement of the thyroid responds 

 to iodine. It is obvious that such a test as Marine and Lenhart have proposed is not 

 applicable to malignant tumors other than the thyroid, as it has long been known in 

 experimental cancer research that transplantable mouse cancer is definitely influenced 

 in its growth by many chemical compounds (Clowes, 1908), particularly the heavy 

 metals. 



Schoene (1910) showed that for a time regression of advanced implanted mouse 

 cancer could be induced by the intraperitoneal injection of iodine and mercury in the 

 form of KI and HgCl 2 . He found the effect of mercury to be much more marked than 

 that of iodine. It was thus known that iodine had an inhibitory effect upon genuine 

 neoplasms and it therefore seemed possible that the action of iodine upon the proliferating 

 thyroid might be due to some specific action upon the tissue, such as these experiments 

 of Schoene's indicated the agent possessed for genuine neoplasms of other organs. 

 Marine and Lenhart reported in 1910 that fish suffering with hyperplasia of the thyroid 

 were favorably affected by adding iodine in the form of Lugol's solution to the water 

 in the troughs in which they were kept, and from these observations applying the theory 

 above stated, concluded that the so-called carcinoma of the thyroid in the Salmonidae 

 was not carcinoma but simple hyperplasia, distinguishable from true neoplasms by the 

 favorable effect of iodine upon the tissue. The remarkable infiltrative character of these 

 neoplasms, so well described by Scott, Plehn, and Pick, and reported in our first prelim- 

 inary reports, Marine explains as due to the absence of a capsule. This feature of 

 the case we have dealt with under the appropriate heading and it need not be again 

 referred to here. 



The results of Marine and Lenhart in causing regression or, as they term it, 

 involution or reversion, of the hyperplastic thyroid in the Salmonidae by the administra- 

 tion of iodine through the water, we have been able to confirm. In order to determine 

 whether the action of the iodine was peculiar to this element and might therefore be 

 looked upon as acting upon the thyroid by virtue of its physiological relation to this 

 organ, in repeating the experiments of Marine and Lenhart we decided to control them 



