Shelf ord. — Fish Poisoning by Gas Wastes 75 



and amphibians are much more resistant than fishes. It 

 is probable that very young fry are as a rule most sensi- 

 tive, but the subject is being investigated further at this 

 point. The most sensitive stage in the life history is the 

 stage with which minimal fatal amounts must be de- 

 termined. 



The investigation showed that gases such as sulphur 

 dioxide, hydrogen sulphide, and ethylene remain in solu- 

 tion in standing water for days in sufficient quantity to 

 kill fishes. Dr. Wells showed that carbon monoxide in 

 particular makes water toxic for weeks. Being retained 

 by water for long periods, it ranks with the most poison- 

 ous solids in toxicity. 



Compounds such as xylene, benzene, phenanthrene, and 

 naphthalene are regarded as insoluble and hence harm- 

 less by some industrial chemists. These proved very toxic 

 and sufficiently soluble to kill fishes in a few minutes, be- 

 ing among the most toxic compounds in the whole series 

 of coal tar derivatives. 



On encountering nearly all these compounds fishes do 

 not turn back as they do in the case of the detrimental 

 substances and conditions which occur regularly in fish 

 waters, but swim into them without noting them and on 

 encountering pure water again they turn back into the 

 polluted water, even though it causes death in a short 

 time. This is true also of the gas liquors studied and of 

 gas in solution and is the rule in both acid and alkaline 

 water. It is obvious from this that these types of contam- 

 inating substances are double dangerous and an earnest 

 effort should be made to prevent their introduction into 

 streams at all. 



