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 n 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 not 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 n. 

 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 1 5-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 oxygen 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. 



Spring 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 1 7.25 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. 



Lack of oxygenation can be excluded from the consideration of causation. 



