1880.] 



MICEOSCOPICAL JOUENAL. 



149 



The Preparation and Mounting 

 of Microscopic Objects. 



III. On page 95 it is stated that 

 rin^ of "sheet-caoutchouc" are 

 useful for mounting diatoms. This 

 is an error: what we intended to 

 say was sheet-gutta-percha, but we 

 did not observe the mistake until 

 after the article was printed. 



In Science for July 17th, there 

 is an article by Prof. H. L. Smith 

 on "Dry Mounts for the Micros- 

 cope," in which he speaks in favor 

 of the sheet-gutta-percha for dia- 

 toms. He also favors shellac rings, 

 and recommends that the shellac be 

 colored by rubbing it up with 

 " diamond black." 



As regards the use of wax in 

 mounting. Prof. Smith was the first 

 to suggest it, but he now writes : 

 "The number of spoiled speci- 

 mens, especially of diatoms and 

 delicate transparent objects which 

 I can now show, proves that this 

 method of mounting is decidedly 

 bad." 



The fault with the method is, 

 that after a time a dew-like deposit 

 will form upon the cover-glass, and 

 perhaps upon the object also. What 

 Prof. Smith writes is the result of 

 long experience, and it is sufficient 

 to lead microscopists to discard the 

 wax-cells entirely, unless they can 

 be covered by some coating of ce- 

 ment, that will prevent the forma- 

 tion of the deposit complained of. 



Prof. Smith also says that a de- 

 posit of a simular character will 

 form, if asphalt is used for the cells. 



In view of all this, the mounter 

 will be puzzled to know what he 

 can use for his cells. It is a difficult 

 question to answer, but we would 

 advise the use of the sheet-gutta- 

 percha for thin cells, shellac for 

 thicker ones, and the curtain-ring 

 cells for the very thick ones, made 

 with wax as described in page 96, 



but with the wax entirely covered 

 with hard balsam dissolved in ben- 

 zole. 



Mounting in Fluid. Among the 

 many processes for mounting in 

 fluid, only two or three of the sim- 

 plest are really good, for with most 

 of them the cement will eventually 

 creep under the cover. "We vouch 

 for the excellence of those here 

 described, if the directions are care- 

 fully followed. 



Fluid mounting is applicable to all 

 objects that are sufficiently transpa- 

 rent. It is advisable when the ob- 

 ject is too delicate for a balsam- 

 mount and its structure is not well 

 shown in the dry condition. 



The fluids employed are usually 

 one of the following solutions : Dis- 

 tilled water ; water with 5-10 per 

 cent, of carbolic acid ; camphor wa- 

 ter ; mixtures of water and glycerin ; 

 pure glycerin ; special preserva- 

 tives. 



The process is the same for all of 

 these, and for any fluid which does 

 not dissolve the cements employed. 



The cell must first be made, and 

 for this purpose shellac is the best 

 cement ; it should be used rather 

 thick, and a very deep cell can be 

 turned up by means of the knife- 

 blade and the turn-table. A num- 

 ber of cells of different depths should 

 be kept on hand, so as to be per- 

 fectly dry and hard when they are 

 wanted for use. 



The objects should be perfectly 

 permeated by the fluid in which 

 they are to be mounted, before they 

 are placed in the cell. The mount- 

 ing is conducted as follows : 



a. Choose a shellac cell of a suit- 

 able thickness, put it on the turn- 

 table and run a layer of benzole- 

 balsam upon it, using a solution that 

 is just thin enough to flow freely. 

 Set aside for about one minute, or 

 until a thin skiu hag formed upon 

 the balsam, 



