236 HAROLD D. CLAYBERG. 



Two 8 candlepower electric lights were fixed above the center 

 of the two halves, i. e., above a point midway between the screen 

 partition in front of the introducer tees and the center drain. 

 The lights were 15-20 cm. above the surface of the water which 

 was 13 cm. deep. The tank and lights were enclosed under a 

 black hood. The experiments were observed through openings 

 in the hood above the lights or through the glass side late at 

 night. Water differing as little as possible from that in which 

 the fish usually live was used for control readings. Controls 

 were observed and the conditions in the two ends of these were 

 the same either because the water introduced at the two ends 

 was alike or because no water was run into either end (standing 

 water). Behavior of both bullhead and sucker in tank controls 

 was of two types identified as quiescence and circuiting. The 

 latter refers to swimming around the tank and involves both 

 back and forth movement and crosswise movement. The cross- 

 wise movement, while ignored in the charts, should be under- 

 stood to occur, especially in the case of controls. In controls 

 quiescence predominated after a short period of circuiting (see 

 Chart I., Bullhead Control). 



In experiments of this kind the reactions of the fish are com- 

 monly graphed, that is the distance between two lines on a sheet 

 of paper (see chart I.) is used to represent the length of the 

 tank. Cross movements of the fish are ignored in the graphing. 

 Vertical distance is used to represent time according to scale. 

 Thus in chart I. control 3 the bullhead went the entire length of 

 the tank twice during the first one minute and 20 seconds. 



For the reaction experiments only suckers (Catostomus com- 

 mersonii) and bullheads (Ameiurus nebulosus) were available, 

 but their behavior is not materially different from that of the 

 standard sunfish (Lepomis humilis). More fish were not ob- 

 tainable on account of the swollen condition of the streams, 

 hence the small number of experiments done. 



2. Reaction and Standardization. Standardization through 

 reaction in gradients would be dependent upon (a) Definiteness 

 of some change in reaction occurring (in case of the fish) ; (b) ac- 

 curacy of the change with reference to concentration; (c) speed 

 of standardization; (d) reasonably low cost of the process. 



