Article VIII. — The Reactions and Resistance of Fishes to Car 

 bon Dioxide and Carbon Monoxide* By Morris M. Wells. 



Introduction 



Carbon monoxide and carbon dioxide are both present in the waste 

 that is diverted into natnral waters by many works where ilkmiinating 

 gas is manufactured and, since the waste as a whole is known to be 

 exceedingly poisonous to aquatic organisms, the role played in its toxic 

 action by the two gases in question was investigated at the time that 

 the many other organic substances of which the waste is composed 

 were studied by Shelf ord.f The investigation has shown that both of 

 the gases are poisonous to fresh-water fishes even when present in 

 the water in relatively small proportions, but the monoxide has been 

 found to be by far the more deadly of the tw^o. 



Carbon dioxide is present normally in the natural habitats of 

 practically all fresh-water organisms, but its toxicity does not mani- 

 fest itself unless it occurs in concentrations which are high as com- 

 pared with lethal concentrations of carbon monoxide. At a concen- 

 tration of 10 c.c. per liter, carbon dioxide will quickly prove fatal 

 to the more sensitive fishes; and it is doubtful if there are any fresh- 

 water fishes that could continue to live in water wh.ere the carbon- 

 dioxide content averaged as high as 6 c.c. per liter throughout the 

 year. On the other hand, there is evidence that a certain small con- 

 centration of carbon dioxide, that is, a certain degree of acidity, is 

 beneficial, if not actually essential to the continued existence of some, 

 and perhaps many, fresh-water fishes. It would not be at all safe 

 to assume that all fresh-water organisms require an environment 

 whose reaction (to phenolphthalein) is slightly acid, for it is known 

 from investigation that certain organisms, as the plankton in fresh- 

 water lakes, seem actually to prefer alkalinity to acidity. Further- 

 more, there are many cases on record where fishes that normally live 

 in water that is slightly acid from the presence of CO^ have continued 



*Contribiitions from the Zoological Laboratory of the University of Illinois, No. 

 107. 



tAn Experimental Study of the EtTects of Gas Waste upon Fishes, with E.«poi-ial 

 Eeference to Stream Pollution. Bv V. E. Shelford. Bull. 111. State Lab. Nat. Hist., 

 Vol. XI, Art. VI, pp. 381-410. 1917. 



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