no 



F. G. HALL. 



the determinations. By this method the changes brought about 

 in the hydrogen ion concentration by substances present in the 

 distilled water were mainly dialyzed from the gland. It is only 

 those substances which do dialyze from the gland that are of 

 concern in this problem. In the first series of experiments the 

 yellow perch was used and a definite amount of gas was removed 

 from the swimbladder (five cubic centimeters) by methods 

 already described in the gas withdrawal experiments, page 83. 

 Care was taken not to injure the fishes more than was absolutely 

 necessary. A very small needle was used and the puncture was 

 made at the opposite end of the swimbladder from the gland. 



TABLE IX. 



DETERMINATION OF THE pH OF THE SWIMBLADDER GLAND OF NORMAL PERCH. 



The gland was allowed to dialyze in 5 c.c. of distilled water free from carbon 

 dioxide, and 3 c.c. was pipetted for the colorimetric determination. 



TABLE X. 



DETERMINATIONS OF THE pH OF THE SWIMBLADDER GLAND OF PERCH FOLLOWING 

 THE WITHDRAWAL OF 5 c.c. OF THE GAS FROM THE SWIMBLADDER. 



A similar amount of the carbon dioxide free water was used as in the deter- 

 minations with normal fishes. The "duration of stimulus" of the decreased 

 internal pressure indicates the time between the withdrawal of the gas and the 

 removal of the gland from the fishes. 



