98 



a Shadbolt's turn-table and some cements. Brunswick black and 

 asphaltum, or gold size, are recommended by the European writ- 

 ers, and I have sometimes used a preparation of fine red sealing- 

 wax dissolved in alcohol, or a mixture of asphaltum, pitch, and 

 gutta percha, made by dissolving asphaltum in turpentine until it 

 will take up no more ; this is strained through fine muslin, and 

 pitch added to the liquid, so as to make, when it is dissolved, a 

 composition about as thick as Canada balsam. To this a few 

 pieces of gutta percha are added, and it is allowed to stand in a 

 covered vessel until it becomes thick enough for use, which may 

 be known by its dropping only with some difficulty from the 

 camel's-hair pencil used to place it on the slide. For mounting 

 Diatoms in their recent state, so as to exhibit the stipes in the 

 stipitate species and the endoehrome in all of them, a mixture of 

 equal parts of proof spirit and distilled water will be found use- 

 ful. For some species I have found an excellent medium to be 

 Mr. Farrant's compound of glycerine and gum Arabic,* it pre- 

 serves the endoehrome of the Diatoms and the plant on which 

 they are found growing intact and of its natural appearance. 

 For some species, however, it will not do, as it renders them so 

 transparent that they are with difficulty visible. 



I will now proceed to specify the different methods of mount- 

 ing Diatoms separately ; lettering them so that they may be 

 referred to. 



A. We wash the gathering in fresh water, which has been 

 either distilled, or, at least, filtered, and separate the heavier from 

 the lighter species. We shake the gathering violently in a large 

 quantity of water, and almost immediately pour it off; this 

 removes all sand and gravel. The Diatoms are allowed to set- 

 tle, and the water is poured off after about an hour's standing. 

 Enough fresh water is now poured over them to make a height 

 of two inches in the glass, and it is allowed to stand for twenty, 

 or at most thirty minutes. The water being carefully removed, 

 it carries with it the mud and portions of broken valves. Even 

 the smaller species will subside through two inches of water in 

 thirty minutes, but, as Dr. Arnott remarks in a letter to the pres- 

 ent writer, " such as Odontidium parasiticum and a few other 

 minute things may require an hour, as they lurk among the mud, 



* Lond. Mic. Jour. Vol. VI. p. 118. 



