54 Nature of Aquatic Enviro^iment 



lake to the blood of the animal body. As the cells of 

 the body take from the blood such of its content as is 

 suited to their need, so the plants and animals of the 

 water renew their substance out of the dissolved sub- 

 stances the water brings to them. 



Organic substances dissolved in the water may so 

 affect both its density and its viscosity as to determine 

 both stratification and distribution of suspended solids. 

 This is a matter that has scarcely been noticed by 

 limnologists hitherto. Dr. J. U. Lloyd ('82) long ago 

 showed how by the addition of colloidal substances to a 

 vessel of water the whole contents of the vessel can be 

 broken into strata and these made to circulate, each at 

 its own level, independent of the other strata. Solids 

 in suspension can be made to float at the top of particu- 

 lar strata, according to density and surface tension. 



Perhaps the "false bottom" observed in some north- 

 ern bog-bordered lakes is due to the dissolved colloids 

 of the stratum on which it floats. Holt ('08, p. 219) 

 describes the "false bottom" in Sumner Lake, Isle 

 Royal, as lying six to ten feet below the surface, many 

 feet above the true bottom ; as being so tenuous that a 

 pole could be thrust through it almost as readily as 

 through clear water; and as being composed of fine 

 disintegrated remains of leaves and other light organic 

 material. "In places there were great breaks in the 

 'false bottom,' doubtless due to the escape of gases 

 which had Hfted this fine ooze-like material from a 

 greater depth: and through these breaks one could 

 look down several feet through the brownish colored 

 water. ' ' 



Perhaps the colloidal substances in solution are 

 such as harden upon the surface of dried peat, like a 

 water-proof glue, making it for a time afterward imper- 

 vious to water. 



