232 MORRIS M. WELLS. 



specific reaction may be in part a matter of size, as the crappies 

 and sunfishes averaged larger than the blue-gills. Small sun- 

 fishes were, however, found to be less sensitive to CO 2 than were 

 blue-gills of the same size. In this case the reaction is correlated 

 with resistance as the sunfishes are more resistant than the blue- 

 gills. The bullheads, however, are perhaps the most resistant 

 of our fresh water fishes yet they are very sensitive to CO 2 . 

 The sensitiveness of the bullheads is probably related to the 

 peculiarity of their integument which (Herrick, '02) has chemical 

 perceptors "taste buds" scattered over its entire surface. 



So far the fishes had for the most part selected the end of the 

 tank containing the largest proportion of neutral water, i. e., 

 the lowest acidity. To ascertain definitely the reactions to the 

 neutral water, the following experiments were performed. 



(4) Slightly Add (j c.c. C0 2 per Liter) vs. Neutral Water.} 

 The slightly acid water was obtained by partially aerating the 

 water which flowed into one end. This was done by running it 

 through a galvanized tank which was a part of another piece 

 of apparatus. The gradient tested practical neutrality at one 

 end, and slight acidity at the other. The fishes definitely se- 

 lected the end containing the CO 2 and were thus negative to 

 the neutral water. 



(b] Reactions to Sulfuric Acid. It should be pointed out 

 that experiments where other acids than H 2 CO 3 are added to 

 water, which contains bicarbonates, are open to misinterpre- 

 tation if an attempt is made to compare the reactions of the 

 animals to the acids, in this way. The addition of a strong 

 mineral acid to such water does not result in the presence of a 

 hydrogen ion concentration from the mineral acid itself, until 

 all the bicarbonates have been decomposed (i. e., changed to 

 sulfates, etc.) or, in other words, not until the water has become 

 acid to methyl orange. The reaction is a double decomposition, 

 H 2 SO 4 + Ca(HCO 3 ) 2 l;CaSO4 -f 2H,CO 3 . Until this reaction 

 is completed, the chief result of adding the mineral acid 

 will be to increase temporarily the concentration of carbonic 

 acid by liberating the fixed and half bound CO 2 . The concen- 

 tration of H ion from this weakly ionized acid will be but a small 

 per cent, of that which would have been obtained from the min- 



