464 
BULLETIN OP 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 (1910b, p. 20; 1911a, 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 HgClj. 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 
