150 THE MICROSCOPE. Nov 
Although some of the samples of the reservoir water 
contained as many as twenty million individuals to the 
gallon, yet it would require many hundred gallons of the 
water to get enough of the oily product which imparts 
taste and odor, to work upon in the laboratory to accu- 
rately determine its nature. 
In the month of August, when the trouble was at its 
worst, the water had a white appearance and was filled 
with minute white threads. On standing, it threw down 
a floculent deposit of a stringy, whitish or yellowish 
white matter. Under the microscope, this deposit was 
found to consist of innumerable Asterionella matted 
togetehr with other diatoms strung together in threads 
the other diatoms, being more especially Melosira, Tabel- 
laria and Synedra. These thread-like forms have not 
been noticed to produce the objectionable taste and odor 
secreted by the Asterionella, and, moreover, they were 
vastly less abundant. The water itself was colorless, the 
apparent color being due to the suspended organisms. 
Neither can it be got rid of by filtration through paper 
or cotton ora thin layer of sand. Sand will arrest nearly 
all the Asterionella. To remove both the Asterionella 
and all the taste and odor arising from it, it is necessary 
to filter through animal charcoal or thorough a properly 
constructed sand filter of sufficient depth. 
The most characteristic feature of the diatom is its 
envelope of silica. There are many other kinds of mic- 
roscopic organisms represented in the different portions 
of the Brooklyn water supply, such as green alga, the 
bluish green alge and the fungi, Rhizopods, Rotifers, 
Crustaceans, etc., but none of these are characterized by 
the presence of silica, and do not in the same sense im- 
peratively demand it as a constituent of their food. 
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 
