134 American Fisheries Society 



The effect of aeration on the various substances used was not 

 always the same. It would appear that the aeration increased 

 the toxicity of crude oils. Sample No. 5899 as noted before did 

 not appear to effect the fish because of its chemical nature, but 

 after continued aeration emulsification occurred and the resulting 

 emulsion then coated the gill membrane, preventing proper respira- 

 tion. This, however, must be looked upon as merely a mechanical 

 change, due to the constant agitation of the oil and water as the 

 air passed through it. Comparatively large bubbles were 

 employed in aeration as the outlets of the aeration apparatus 

 were pinholes in the ends of glass tubes, thus the contents of the 

 jars was constantly stirred. 



In a few experiments in which the light fuel oil obtained from 

 t'fye Brookline, Mass., Board of Health, was employed; the water 

 was not aerated, but changed as soon as the fish began to show 

 any signs of insufficient oxygen supply. As has been before noted, 

 the fish fed regularly and no signs of distress were shown. Con- 

 trols, using fish of about the same weight, and employing the same 

 volume of water having the same surface area exposed, showed 

 that the oil-film caused little, if any, difference in the amount of 

 oxygen absorbed from the atmosphere. The oil did not form a 

 continuous film over the entire surface of the water, but had a 

 tendency to form films at intervals, thus leaving considerable of 

 the surface of the water directly in contact with the air. 



It is very doubtful if, in the small amounts used in mosquito 

 campaigns, the oil would effect the absorption of oxygen from the 

 atmosphere by the water. 



In cases of some of the creosote solutions, aeration decreased 

 their toxicity. This is probably due to an oxidation of the oils 

 themselves. 



When tars, in drainage from roads, are carried into the streams, 

 such drainage undergoes active aeration and agitation sufficient 

 to cause emulsification of oils similar in nature to the crude oils 

 used in the experiments. The small volume of such an emulsion 

 entering a stream would scarcely be sufficient to affect the fish 

 for the effect is undoubtedly a mechanical one in that the emulsion 

 coats the gills and inhibits respiration, or else coats the food of 

 the fish, causing them to ignore it. The emulsion being less dense 

 than the water, would tend to be carried off on the surface in a 



