14 American Fisheries Society 



mostly herring, and were, of course, themselves held in 

 sea water. These tumors were found by Dr. Paul Von- 

 willer, a Swiss student, working in Naples. Since hith- 

 erto no marine fish in sea water has been known to show 

 a thyroid tumor, and since iodine has a marked remedial 

 influence on such growth in fresh water, this find at Na- 

 ples is of unusual interest. The sea water contains ap- 

 preciable iodine, in amounts much greater than those 

 effective in fresh water. Yet the tumors originated and 

 progressed in the presence of this iodine content. 



In Germany, trout culture is widely and extensively 

 practiced, but there the thyroid tumor is practically un- 

 known. Fish so affected are perhaps as often found in 

 the natural streams as in trout hatcheries. The Ger- 

 mans have, with respect to feeding, a regime quite dif- 

 ferent from that which obtains here. In the first place 

 sea fish as a food for trout is largely used. Second grade 

 codfish is cheap, and with other members of the cod fam- 

 ily has become almost a staple food among the hatcheries. 

 A small quantity of shrimp is added to the fish by some 

 breeders. In the second place it is almost or quite a uni- 

 versal practice to cook the food that is fed to trout, whe- 

 ther it consists itself of fish, or the organs and offal of ani- 

 mals. Sea fish, no doubt fresh water fish also, used as 

 a food, and the cooking of meat used as food, are both 

 practices having at least a tendency to prevent thyroid 

 disease. When both are combined the rarity of thyroid 

 tumor in German hatcheries ceases to cause surprise. 

 There are very few, if any, hatcheries in Germany where 

 artificial propagation of trout is based on raw meat food. 

 One may plausibly infer that these two practices are 

 wholly or chiefly the cause for the freedom of Germany 

 from thyroid tumor, and we may suppose that raw meat- 

 fed fish would there acquire the tumors as they do here 

 and in other countries, although this is not necessarily 

 true. I have recently heard that feeding tests which 

 should determine this question have been begun during 

 the past summer in Germany near Munich. 



