1897J MICROSCOPICAL JOURNAL. 321 



Bacillaria require? Multiplied observations in many 

 localities have shown that such a stupendous growth as 

 the reservoirs exhibited last summer is jjossible only 

 when there is present an abundant supply of food in the 

 form of assimilable nitrogen. 



Why should this transformation of ammonia, nitrites 

 and nitrates into nitrogen and the immense multiplica- 

 tion, of Asterionella take place in the reservoir, and not 

 in some pond or stream where Asterionella are found, 

 and where abundance of food is likewise present? To 

 explain this it is necessary to have recourse to what is 

 known of the habits of life of the Asterionella in cases 

 where its enormous multiplication, along with the ac- 

 companying taste and odor have been observed. Its 

 multiplication is essentially favored by abundant access 

 of light; by a gentle, tremulous motion in the water, and 

 by storage in shallow reservoirs. All of these conditions 

 exist in an convenient degree in the Brooklyn reservoirs. 

 Together with the kind and quantity of food they are 

 ample to explain what occurred in an aggravated form 

 last summer, what is observable now, although to a far 

 lesser extent, and what will occur at different seasons in 

 the future until the physical conditions that render the 

 occurrence possible have been removed. 



So far as is known the only remedy which has proved 

 effectual has been that of excluding the light, and con- 

 verting the reservoir into a substantially subterranean 

 basin. The proposal to aerate the water, which was ad- 

 vocated last summer, was fortunately, not entertained. 

 Prof. Leeds speaks with the more positiveness upon the 

 subject inasmuch as he introduced the mechanical aera- 

 tion of water supplies, and has seen its introduction 

 followed by the happiest results in cases where condi- 

 tions favorable to stagnation were dominant. But the 

 reverse of such conditions exists in the present instance, 

 and the aeration of the water in the Brooklyn reservoirs 



