486 
BUI.LETIN OF THE BUREAU OF FISHERIES. 
thyroid enlargement. A bag of pond-io mud was now plaeed 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, 1911, 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 alveoli, 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 epithelium. 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 litter 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- 10 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 liver, 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, 1911, 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 iii.) 
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, 1912, was terminated 
