96 



F. G. HALL. 



used instead of carbon dioxide the volume of the fish does not 

 increase, but on the contrary shows a decrease. Fig. 6 shows 

 a graph obtained when lactic acid was added to the water (i riooo). 

 The effects produced by the lactic acid is probably one of con- 

 striction of tissues caused by the acid; the effect of carbon 

 dioxide is probably due to diffusion of the gas into the swim- 

 bladder. 



IO 

 CX.TtX. 



12. 



to 



2. 3 

 Time 



FIG. 3. A graph to show comparisons of the dissolved gases in the water with 

 the gases in the swimbladder with variation of the dissolved gases. The swim- 

 bladder gases are expressed in percentages and the dissolved gases in cubic centi- 

 meters per liter. A single experiment is represented in the graph. Perch were 

 placed in an aquarium containing normal lake water and the carbon dioxide 

 gradually increased. The time intervals are expressed on the abscissa and the 

 amounts of the gases expressed on the linear scale of the ordinate. 



The fact that fishes change their volume when subjected to 

 water containing high amounts of carbon dioxide may be of 

 ecological importance. In many lakes the amount of carbon 

 dioxide dissolved in the water increases with depth. The 

 oxygen decreases with depth and near the bottom may be 



