EFFECT OF ETHER AND CHLOROFORM ON FISHES. 235 



definite standards a distinct form of behavior should appear or 

 disappear at a definite concentration. 



2. Time till definite symptoms of sickness appear might be 

 used. Such a condition for serial concentrations is shown to 

 the left in chart II. 



3. Killing time is the only standard thus far applied. 



In connection with killing it is our purpose to point out that 

 the time-concentration curve is probably an hyperbola which, 

 if fully demonstrated for a few substances, will render the 

 investigation of drugs in general much easier. 



II. REACTIONS. 



i. Materials and Methods. The reaction experiments were 

 performed in the Shelford gradient tank. This is a tank 122 cm. 

 long by 15 cm. wide by 13 cm. deep. Water is allowed to flow in 

 at each end at a definite rate. It enters the tank through two 

 tees, the cross bars of which are perforated with small holes so 

 as to distribute the inflow throughout the width of the tank. 

 It flows out at the middle at both top and bottom so the two 

 kinds of water meet at the center. In these experiments normal 

 water was run in at the left end at a rate of about 450 c.c. per 

 min. and normal water plus ether or chloroform was run in at 

 the right end at an equal rate. The drug solution was made 

 up in an 1 8-liter bottle, placed above the apparatus, and siphoned 

 out. Siphon and bottle were closed on account of the volatility 

 of the poisons used. To be certain that the concentration under 

 observation remained constant, the flows were tested occasionally 

 throughout the experiment; hence the concentrations quoted are 

 presumably accurate. The outflow at the center did not pre- 

 vent the mixing of the two kinds of water and thus the middle 

 section equal to one half or third of the tank, was a gradient 

 between the normal water and water plus ether or chloroform. 

 Accordingly as a fish moved from left to right in the tank it 

 encountered a gradually increasing concentration of the poison. 

 We found no evidence that fish react to the slight current through 

 the tank. Since each half of the tank held about 9 liters, it 

 required 21 minutes to fill it or to replace all the water in one 

 of the halves. 



