1897] MICROSCOPICAL JOURNAL. 319 



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 othe^r diatoms, being more especially Melosira, Tabel- 

 laria and Synedra. These thread-like forms have not 

 been noticed to produce the objectionable taste and odro 

 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. 

 The oily taste-prodacing substance is volatile and cannot 

 be gotton rid of by distillation. It distills over with the 

 steam, giving to the distilled water a faint whitish 

 appearance or opalescence, and communicates to it the 

 same characteristic taste and smell. 



Neither can it be got rid of by filtration through paper 

 or cotton or a thin layer of sand. Sand will arrest nearly 

 all the Asterionella and then on being washed with pure 

 water, the water used in washing and containing the 

 plant will be found to have taken up the taste and odor. 

 To remove both the Asterionella and all th6 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 algae, the 

 bluish green algae 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. 

 Moreover, the number of non-silex-secreting organisms 

 is insignificant when compared with the stupendous 

 number of diatoms. Thus Prof. Leeds says, but he for- 



