American Fisheries Society 387 



these things are the essentials of domestication with which 

 the tumor especially associates itself. To practice these 

 measures would be an abatement of domestication and in a 

 sense and to a degree would amount to killing the patient, 

 since it is the disease as affecting domestication that is 

 important rather than individual fishes. This may possibly 

 be necessary in the end, but what is needed is something 

 consistent with intensive breeding. Domestication simply 

 must increase the ratio of fish to water over the conditions 

 obtaining in nature, and thus far an inexpensive natural 

 food has not made its way on a large scale in fish culture. 



Thyroid gland is known to have a specific affinity for 

 iodine and the observations of Marine and Lenhart in con- 

 junction with the Pennsylvania Department of Fisheries 

 have shown that the thyroid in its early or microscopic 

 enlargement reacts with iodine in the direction of a reversion 

 toward the normal structure. We have corroborated this 

 during the past summer and have also exposed visible 

 tumors to the action of potassium iodide for thirty days. 

 With these the results are not uniform, some showing con- 

 siderable decrease in size, others remaining unchanged. 

 This is in accordance with the view of a process in which 

 both goiter and cancer is concefned, the tumor tending to 

 lose its response with the increase of its cancerous character. 



We have also found during the past summer that the 

 same results in the way of reversion of structure and reduc- 

 tion of the visible tumor are obtained with mercury as 

 with iodine and somewhat more rapidly. Mercury is not 

 known to react specifically with thyroid and therefore it is 

 at least questionable whether the action of iodine on the 

 enlargement is due to its specific relation to thyroid tissue. 

 It is as reasonable to assume an antiseptic action, not in 

 tlie water, for the changes occur at great dilution, one part 

 to five million parts of water, but cumulatively in the en- 

 larged gland itself. In fact, the rapid reduction of the 

 tumors by these elements, for one of which the thyroid is 

 Icnown to have a special affinity, and both of which are 



