224 ILLINOIS ACADEMY OF SCIENCE 



may occur; (c) length of time required for development of 

 the larva in the intermediate host; (d) seasonal changes in the 

 food habits of the final host, or active migrations of the host 

 to and from sources of infestation. 



RESISTANCE AND REACTIONS OF FISHES TO 



POISONOUS POLLUTING SUBSTANCES FROM 



THE MANUFACTURE OF ILLUMINATING 



GAS. 



ABSTRACT 



By V. E. Shelford, Illinois State Laroratory of Nat- 

 ural History j Urbana 



One of the most important sources of stream pollution 

 viewed from the standpoint of fishes is wastes from the man- 

 ufacture of illuminating gas. Illuminating gas, gas liquor, 

 and thirty-four organic compounds representing the chief 

 classes of compounds found in coal tar and gas liquor have 

 been studied (carbon monoxide and carbon dioxide by Dr. 

 Wells). All the mixtures and all but three of the single com- 

 pounds (methane, acetylene, and anthracene) are very poison- 

 ous to fishes. A surprising feature of the investigation is (a) 

 that compounds which are gases and which would be expected 

 to diffuse out of water rapidly and leave it harmless, as, for 

 example, carbon monoxide, remain in standing water for sev- 

 eral weeks and continue to kill fishes, and (b) that substances 

 which are commonly regarded as insoluble in water, such as 

 naphthalene and benzene are among the most toxic of all. Thus 

 considering the physical properties of these compounds (gases, 

 volatile liquids and solids) it is obvious that the various meth- 

 ods of treating and recovering by-products will almost cer- 

 tainly deliver some poisonous compounds into streams. 



Usually the toxicity of compounds is greatest for the small- 

 est fishes, or in other words, the smaller fishes are most easily 

 killed by the poisons. This is true down to the smallest fry 

 studied. The relative toxicity of over thirty compounds has 

 been determined, but as yet no attempt to determine the mini- 



