94 THE MICROSCOPE. 



on with advantage, in order to prevent effectually the admission of air 

 into the cell, or the escape of fluid out of it."* 



I would remark, that the gold-size employed should be of the 

 consistence of treacle ; when purchased, it is usually too fluid, and 

 should be exposed for some time in an open vessel ; a process which 

 renders it fit for use. In mounting the Desmidiece, great attention is 

 necessary to exclude air-bubbles, which cannot be avoided unless the 

 fluid completely fills the cells ; 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 mois- 

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

 preference to any other mode. A thin description of glass is manufac- 

 tured expressly for the purpose of covering specimens when mounted. 



The rarer species of Desmidiece are frequently scattered amongst 

 decayed vegetable matter, so that it is difficult to procure good speci- 

 mens 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 Desmidiece 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 can 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 occasionally peels off 

 the glass after the specimen has been mounted for some time. To obvi- 

 ate 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, com- 

 posed of japan varnish or gold-size. 



* Mr. Penney, of 251 Tottenham Court Road, supplies an excellent varnish, called 

 " Coachmaker's Black," 



