REACTION AND RESISTANCE OF FISHES. 243 



An experiment with small bullheads is very interesting. 

 Normally the bullheads are perhaps the most resistant fresh- 

 water fishes known. In the reaction experiments they selected 

 a rather low concentration of hydrogen ion but were decidedly 

 on the acid side of neutrality. In the pure distilled water a 

 bullhead (4 in. long) lived 8 days; another in distilled water 

 made .00005 N acid, lived for 20 days. 



(2) Resistance to Doubly Distilled Water. This water was less 

 toxic to the crappies than was the once distilled water, as it 

 contained less colloidal copper. It has been pointed out that 

 the toxicity of the once-distilled water was lessened by the 

 addition of acid, partly because the acid precipitated the col- 

 loidal copper. The experiments indicate further, however, that 

 the neutrality of the water must be reckoned with also. This is 

 again brought out, and more definitely, by a few experiments 

 with the twice-distilled water. A quantity of this water was 

 placed in a large bottle and a solution of barium hydroxid was 

 suspended over it. At the end of a week the water was practically 

 neutral. Two portions were taken in 500 c.c. Erlenmeyer 

 flasks and a small bullhead (2.5 in.) placed in each. One portion 

 was left neutral and the other made slightly acid with HoSO4. 

 The fish in the neutral water lived 16 days and the one in the 

 acid water 19 days. A few other experiments were performed 

 with the twice-distilled water and all gave similar results. The 

 stock of fishes was about exhausted, however, and further ex- 

 periments were delayed until another time. 



V. GENERAL DISCUSSION. 



The fact that in natural bodies of water the chemical reaction 

 of the water may vary from alkalinity through neutrality to 

 acidity or the reverse, makes the practical importance of a knowl- 

 edge of the reactions and resistance of fishes and other organisms 

 to such chemical conditions an obvious one. From the experi- 

 ments and discussion which have gone before, it is clear that 

 water which gives an alkaline reaction to phenolphthalein for 

 any length of time during the year, is undesirable as a home 

 for most fresh-water fishes. On the other hand, marine fishes 

 (Shelford and Powers, '15) with the exception of the anadro- 



