401 



a rule. When in solution the gas forms a very weak acid which would 

 tend to cause fishes to react positively especially in alkaline water. The 

 negative reactions are less definite than to carbon dioxide and other 

 stimuli often encountered in natural environments of the fishes (Chart 

 III, graphs 27 and 28). 



Sulphur dioxide. 



This gas was determined in the Champaign waste which showed 

 in sample without tar 13.84 cc. per liter and sample with tar 56.21 cc. 

 per liter. For the experimental work a tank of Kahlbaum's compressed 

 gas was obtained from the University of Illinois chemical store room 

 and the tank was attached to the gas introducer direct. 



It is very irritating to the mucous membrane and the respiratory 

 tract. It is generated in the burning of sulphur and its characteristic 

 odor is familiar. In the case of fishes, gulping or other similar move- 

 ments indicates its irritating character. Their respiration is usually 

 heavy and they swim around in an intoxicated state for some time be- 

 fore death. A strong solution killed fishes after standing in a battery 

 jar for over two weeks. Weigelt found that 0.0005% solution killed 

 trout in a little more than one hour. 



Fishes are usually negative to higher concentrations from 10 to 

 500 cc. per liter which produce death in a few minutes, but are quite 

 generally positive to concentrations which are fatal in an hour (Chart 

 III, graphs 29 and 30). 



Carbon bisulphide. 



It occurs commonly in crude benzene, and in the tars and other 

 residuals. Known quantities were dissolved in 4 liters of water. It 

 is a powerful poison to man, the vapor producing hysterical neurosis 

 and the liquid taken internally produces unconsciousness quickly. In 

 the case of fishes the symptoms are not markedly different from those 

 caused by a number of other substances ; they appear to become in- 

 toxicated rather slowly. 



In .05 cc. per liter of water fishes were intoxicated but recovered 

 after an hour and a half. The experiment was performed in a closed 

 bottle so that evaporation could hardly be responsible. It is possible 

 that the substance was absorbed or rendered harmless by some tissue 

 such as fat. 



Two species of sunfish were tried in the gradient tank and both 

 were positive to fatal concentration while the minnow (Pimephales) 

 was negative (Chart III, graph 29 and 30). 



