420 
bulletin of the bureau of fisheries. 
the disease is developed. It is in our opinion highly improbable that any of the factors 
in causation of the disease are to be found among the variations of the concentration 
in which the common earth salts and other matter are found in these waters. 
None of the analyses shown in table ii disclose any trace of iodine or bromine, but 
only ordinary volumes, as a single liter, were devoted to the reactions for these elements. 
In order to test further the presence of these elements in the water of the Craig Brook 
station, where a large part of our data has been obtained, we have had two samples of 
15 liters each used entirely by the Bureau of Chemistry for determining iodine and bro- 
mine in two sources of water at the Craig Brook station. The Craig Pond water (no. 
5867) is the chief water supply of the Craig Brook station. It is slightly augmented, 
before reaching the fish ponds, by small volumes of spring water riot subjected to anal- 
ysis. The farm-house spring, whose complete content is not shown, is a minor supply 
arising on the station grounds, and is probably typical of the springs of the immediate 
neighborhood, such as the lawn spring (no. 5868) whose content appears in table ii. 
The Craig Brook water itself is in this way shown to contain i part of iodine to 
1,310,000,000 parts of water; and i part of bromine to 149,000,000 parts of water. The 
farm-house spring showed about the same quantities of each element: of iodine, i part 
to 1,250,000,000; of bromine, i part to 142,800,000. The ratio of iodine to bromine 
was the same in the two sources, i to 8.7. As the delicacy of the iodine test detects 
about one one-hundredth milligram of iodine, the 15-liter sample contained a little more 
than enough for the reaction. 
Since thyroid hyperplasia begins in the Craig Brook water and is reduced by iodine 
in dilutions which, though much attenuated, are yet much richer in iodine than the 
above, it seems certain that the extreme dilution of iodine found to occur naturally in 
the water is without appreciable physiological effect. Most brook water will probably 
be found to contain iodine in quantities comparable to those in Craig Brook. 
Dissolved oxygen . — No lack of dissolved oxygen contributes to the thyroid disease 
at the Craig Brook station. Flowing brooks almost invariably contain all the oxygen 
the water will absorb from the air. The Craig Brook water was several times titrated 
for oxy^gen and was found to be air-saturated. The water at the outlets of troughs and 
cement tanks containing trout was likewise examined and the amount of oxygen removed 
by the fish was determined. A cement tank containing about 40 wild trout diminished 
the oxygen content by 0.13 cubic centimeter per liter. Sixty-eight yearling trout held 
in a wooden trough removed 0.4 cubic centimeter of oxygen per liter, leaving an oxygen 
content of 6.8 cubic centimeters per liter at a water temperature of 15° C., which is barely 
short of air-saturation. 
vSpring waters not infrequently emerge from the earth with a considerable deficiency 
of oxygen. One such was found draining into Craig Brook, holding only 2.39 cubic 
centimeters per liter at 17. 25°C., which is about 35 per cent of air-saturation. Its volume 
was insignificant, and no additions of this sort to the stream perceptibly affect its 
oxygenation. 
Tack of oxygenation can be excluded from the consideration of causation. 
