REACTION AND RESISTANCE OF FISHES. 22J 



animals in aerated water, which was thus saturated with oxygen 

 (5-5 to 7 c.c. per liter) while the free carbon dioxide was removed. 

 If aerated sufficiently, the Illinois tap water becomes alkaline 

 to phenolphthalein, and upon writing to Allee with regard to 

 this matter he gives me permission to state that he kept his 

 stock of isopods in such alkaline water for a period of 22 weeks, 

 without increased mortality. He points out that the per cent, 

 of rheotactic response, after a large number of trials, was 8 per 

 cent, less than at Chicago but does not know whether or not to 

 regard this as significant. 



Table I. shows that Illinois water contains 18 c.c. of CO 2 

 per liter and practically no oxygen. Either of these conditions 

 would alone prove fatal to fishes, while the combination would be 

 doubly fatal (Wells, '13). Since aeration removes the CO 2 and 

 at the same time saturates with oxygen, it was thought that this 

 would fit the water for supplying the fish aquaria. The water as 

 it came from the tap was therefore run through the aerating pans 

 which form a part of the apparatus described by Shelford and 

 Allee ('13). The device consists of a series of galvanized pans, 

 placed one beneath the other. The water runs into the upper 

 pan and trickles down through successive pans into a galvanized 

 tank. From the tank, pipes lead to the aquaria. The flow 

 into two large aquaria was regulated to 500 c.c. per minute for 

 each and the fishes were now brought in from the nearby streams 

 and placed in the aquaria in rather large numbers. The aquaria 

 were 8 ft. x 2 ft.; about 300 small fishes were placed in each. 

 This was overcrowding, but fishes have been kept successfully 

 for some time, in closer quarters at Chicago. 



The immediate mortality of the stock was not great. It was 

 noted that the darters and other more sensitive fishes did not 

 live well but the sunfishes, bullheads and minnows seemed to be 

 normal. In a few days, however, these fishes began to die. 

 It was thought that the water contained too large an amount of 

 carbonates and an arrangement was made to introduce sulfuric 

 acid into the aerated water at the galvanized supply tank. 

 Enough acid was added to convert about one third of the carbon- 

 ates into sulfates and with some benefit. It had been noted in the 

 experiments that the fishes did not swim about as actively as 



