28 PREPARATION AND MOUNTING 



moved, and so present every part of the object to the eye save 

 that by which it is fastened to the disc. On this account it is 

 often made use of when some particular subject is undergoing 

 investigation, as a number of specimens may be placed upon the 

 discs with very little labour, displaying all the parts. But where 

 exposure to the atmosphere or small particles of dust will injure 

 an object, no advantage which the discs may possess should be 

 considered, and an ordinary covered cell should be employed. 

 Small pill-boxes have been used, to the bottom of which a piece 

 of cork has been glued to afford a ground for the pin or other 

 mode of attachment ; but this is liable to some of the same faults 

 as the disc, and it would be unwise to use these for permanent 

 objects. 



Messrs. Smith and Beck have lately invented, and are now 

 making, a beautiful small apparatus, by means of which the disc 

 supporting the object can be worked with little or no trouble into 

 any position that may prove most convenient, whilst a perforated 

 cylinder serves for the reception of the discs when out of use, 

 and fits into a case to protect them from dust. A pair of forceps 

 is made for the express purpose of removing them from the case 

 and placing them in the holder. 



All dry objects, however, which are to be preserved should be 

 mounted on glass slides in one of the cells (described in Chapter 

 I.) best suited to them. Where the object is to be free from 

 pressure, care must be taken that the cell is deep enough to en- 

 sure this. When the depth required is but small, it is often 

 sufficient to omit the card, leather, or other circles, and with the 

 " turn-table " before described, by means of a thick varnish and 

 camel-hair pencil, to form a ring of the desired depth ; but 

 should the varnish not be of sufficient substance to give such 

 " walls " at once, the first application may be allowed to dry, and 

 a second made upon it. A number of these may be prepared at 

 the same time, and laid by for use. When liquids are used (see 

 Chapter IV.), Dr. Carpenter recommends gold-size as a good 

 varnish for the purpose, and this may be used in " dry" mountings 

 also. I have used the asphaltum and india-rubber (mentioned in 

 Chapter I.), and found it to be everything I could wish. The 

 cells, however, must be thoroughly dry, and when they will bear 



