72 PREPARATION AND MOUNTING 



the operator's clothes may ensue. The nearly decolorized 

 liquid must now be diluted with a considerable quantity of 

 water, and the deposit allowed to subside, the supernatant 

 liquid poured off, and the process of heating with sulphuric 

 acid and addition of chlorate of potash repeated until the 

 sulphuric acid occasion no further blackening; then the 

 cleaning may be finished in the usual way by washing." 



I have had many complaints from my friends that with 

 all their care they have found nothing fit for mounting in 

 guano. This is readily accounted for by one fact, that not 

 one sample in twenty of what is called guano in the market 

 has an atom of guano in it. Procure real guano, and you 

 will get real returns. 



The fossil Infusoria (as they were formerly called) are now 

 termed Diatomacea9, and are found in various parts of the 

 world ; such as Bermuda earth, Berg-mehl from Norway, the 

 deposit from Mourne Mountain in Ireland, &c. They are 

 found in immense quantities, and afford the microscopist 

 innumerable objects. The same treatment as that usually 

 employed for the DiatomaceaB must be followed with these 

 deposits ; but as they are sometimes obtained in hard masses, 

 disintegration is first necessary. To effect this, they are 

 usually boiled for a short time in diluted liquor potasses, 

 which will soon cause the mass to fall into a mud-like 

 deposit. Water must then be immediately added, in order 

 that all further action of the liquor potasses may be stopped, 

 otherwise the objects searched for will be dissolved. For this 

 reason it is necessary to understand what substance is being 

 dealt with, because some deposits are much finer and are 

 acted upon more readily than others. 



In mounting these objects, some are so delicate that they 

 are almost invisible when balsam is used with them ; they 

 are therefore usually mounted dry. Others, however, are 

 much coarser, and may be mounted in balsam like the Diato- 

 maceas mentioned in Chapter IV. 



The common Infusoria cannot be mounted dry with any 

 great success, though a few may be placed upon the glass 



