230 THE MICROSCOPE. 



an open vessel ; a process which renders it fit for use. In 

 mounting the Desmidacece, great attention is necessary to 

 exclude air-bubbles, which cannot be avoided unless the 

 fluid completely fills the ceils ; and also not to use too 

 much fluid, as in this case the smaller species will often be 

 washed away on the escape of the superfluous portion. As 

 the cells cannot be sealed whilst any moisture remains on 

 their edge, it should be removed by blotting-paper, in 

 preference to any other mode. A thin description of glass 

 is manufactured expressly for the purpose of covering 

 specimens when mounted. 



" The rare species of Desmidacece are frequently scattered 

 amongst decayed vegetable matter, so that it is difficult to 

 procure good specimens for mounting. In such cases, a 

 small portion of the mass should be mixed with a little of 

 the creosote fluid, and stirred briskly with a needle. 

 After this has been done, the Desmidacece will sink to the 

 bottom, when the refuse should be carefully removed. 

 Successive portions having been thus treated, specimens 

 will at length be procured sufficiently free from foreign 

 matter. Even in ordinary circumstances, if a small extra 

 quantity of fluid be placed in the cell, and the slide gently 

 inclined, most of the dirt may be removed by a needle 

 before the cell is closed ; which process will materially 

 increase the beauty of the preparation. 



"If the cells are insufficiently baked, the japan occa- 

 sionally peels off the glass after the specimen has been 

 mounted for some time. To obviate this inconvenience, 

 Mr. Jenner previously heats the cell, with much caution, 

 over a rushlight, until the japan becomes of a dark colour, 

 and vapour ceases to arise from it. When gold-size is used 

 for closing the cell, the intrusion of some of it frequently 

 destroys valuable specimens, whatever care may be taken. 

 Mr. Jenner has therefore relinquished it, and now employs 

 a varnish made of coarsely comminuted purified shell-lac 

 or translucent sealing-wax, to which is added rectified 

 spirits of wine, in sufficient quantity to cover it. This 

 varnish will be ready for use in about twelve hours : when 

 it is too thick, a little more spirit should be added. Mr. 

 Jenner applies three coats of this varnish, and about a week 

 afterwards a fourth, composed of japan varnish or gold- 



