REACTION AND RESISTANCE OF FISHES. 225 



(or both) as indicator. The samples were collected by means 

 of a pipette inserted to a given level below the surface, and the 

 titrations were always made at once, with as much care as seemed 

 necessary. For instance samples containing a high concen- 

 tration of CO 2 need to be titrated with rapidity, while samples 

 containing H 2 SO 4 or KOH may be titrated without haste. 



B. RESISTANCE EXPERIMENTS. 



The procedure in the resistance experiments was very simple in 

 most cases. In general the desired solutions were made up from 

 standard solutions of the acid or alkali (measured from burettes) 

 and the fishes introduced. Temperature was controlled by 

 setting the jars containing the solutions, in running tap water. 

 As the experiment proceeded, samples for testing were with- 

 drawn when necessary, and the same amount of water was re- 

 moved from the control. General controls were kept running 

 throughout the entire time, while numerous temporary controls 

 were set up as demanded by individual experiments. 



The species of fishes used principally, have been the blue-gill 

 (Lepomis pallidus), white crappie (Pomoxis annularis), green 

 spotted sun-fish (Lepomis cyanellus), and bull-head (Ameiurus 

 melas). Most of the fishes were caught (by seining) in the small 

 streams in the vicinity of the university (the crappie came from 

 a small artificial lake) ; all were brought into the laboratory 

 with as little handling as possible, and placed at once in large 

 aquaria. They were fed from day to day but fishes do not 

 always eat well in confinement and as time went by they became 

 more or less starved. The changes in the reactions of fishes, 

 which accompany starvation have been investigated and will 

 be discussed in another paper. 



The chemicals used have been the chemically pure prepara- 

 tions of Kahlbaum or the analyzed preparations of Baker. 



III. THE WATER. 



An investigation of the reactions of fishes to salts in solution 

 was begun at Chicago in 1912, at the suggestion of Dr. Shelford. 

 In the fall of 1914 Dr. Shelford left Chicago to take a position at 

 the University of Illinois and the writer accompanied him to 



