486 BULLETIN OF THE BUREAU OF FISHEBaES. 



thyroid enlargement. A bag of pond-io mud was now placed in a pail, which was 

 filled with Craig Brook water and placed in the kennel. The mud was not renewed, 

 but fresh water was poured over it from time to time. The dog was fed a meat diet. 

 July 5, 191 1, the right thyroid gland was found enlarged nearly to the size of a small 

 hen egg. The left gland was palpable but not evidently enlarged. During the next 

 year pond-io mud and water was supplied to the dog, and on July i, 1912, she was in 

 good condition, with both thyroid lobes decidedly enlarged. The left lobe was removed 

 and found to weigh 19.3 grams, its dimensions being 5.5 by 3.5 by 2.75-centimeters. 

 There was no control for this dog. 



Under the microscope the thyroid of dog 24 presents follicles of great size filled 

 with stainable colloid, protruding into which are many bud-like processes. The epi- 

 thelium is columnar in the larger alveoU, the flattened nuclei stain deeply, are oval or 

 spherical, the protoplasm also taking the nuclear stain. The bud-like processes are 

 caused by infoldings of the walls of the alveoli covered with columnar epitheUum. The 

 whole presents the appearance of a gland which has been in a state of active hyper- 

 plasia, but is at present a colloid gland. 



The feeding of these dogs was intended as a preliminary informal trial and was not 

 controlled. Having indicated the probability of positive results in an important field, 

 more accurate experiments were begun with other young dogs. 



A bitch with a Htter of five pups was obtained from the District of Columbia, a 

 nongoitrous region. These were shipped to the Craig Brook station, in October, 1910. 

 The mother and two pups were supplied until the following summer with a pan of mud 

 from pond 10 holding pond-io water supernatant, both kept frequently renewed. The 

 three remaining pups were held as controls and received mud and water from Craig 

 Brook directly, unconnected with fish-cultural conditions. The food for all was shredded 

 wheat scrap and milk until December, when it was changed to dog biscuit with occasional 

 cooked Uver, and this continued until spring, when it was again changed to cereal. The 

 two lots of dogs were separately confined in kennels indoors and were exercised and let 

 loose only under proper restrictions. 



On palpation in July, 191 1, no thyroid enlargement could be detected in any of 

 them. This experiment was now abandoned and a new one instituted with scrapings 

 from the inside of unpainted wooden fish troughs (no. 93), which had long been used to 

 hold domesticated trout and in which thyroid tumors were constantly produced in such 

 trout. (Table in.) 



The three pups formerly used as controls were now given to drink Craig Brook water 

 from a pail containing the fish-trough scrapings suspended in a cheesecloth bag. The 

 material was kept cold by standing it continuously in a trough of flowing cold water. 

 A portion of the clear water from the pail was supplied to the dogs each day. The 

 mother and the two pups which had formerly received pond- 10 mud and water for several 

 months were now used as controls to the experiment with scrapings. They received 

 water taken from the same pail and boiled. All the dogs were fed liver, cooked and 

 uncooked. The experiment began August i, i9ii,and in January, i9i2,was terminated 



