OF MICROSCOPIC OBJECTS. 43 



the hydrochloric, and the heat kept up to almost boiling-point for 

 another hour at least, adding a little fresh acid as before. When 

 this ceases to act, the deposit must be allowed to settle perfectly 

 and the acid poured off. All traces of the acid must now be 

 washed away with pure water, when the remains will be Diatoma- 

 cea3, the sand contained in the guano, and a few other forms. 

 Some of these may be mounted dry, as before mentioned, but the 

 greater portion should be put up in Canada balsam as described 

 in Chapter III. 



Such is the ordinary method for the treatment of guano ; but 

 Mr. Eylands' mode of proceeding with ordinary Diatomaceaj (be- 

 fore given) will be found equally successful with these deposits. 



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

 termed Diatomaeese, and are found in various parts of the world 

 "Bermuda earth," "Berg-mehl" from Norway, 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 Diatomacese must 

 be followed with these deposits, but as they are sometimes ob- 

 tained in hard masses, disintegration is first necessary. To effect 

 this, they are usually boiled for a short time in diluted liquor po- 

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

 posit. Water must then be immediately added, in order that all 

 further action of the liquor potassce 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, be- 

 cause some deposits are much fii>er and 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 there- 

 fore usually mounted dry. Others, however, are much coarser, 

 and may be mounted in balsam like the Diatomacese mentioned 

 in Chapter III. 



The common Infusoria cannot be mounted dry with any great 

 success, though a few may be placed upon the glass slide and 

 allowed to dry naturally, when their characters will be very well 

 shown. To obtain anything like a natural appearance, they must 

 be put up in fluid as in Chapter IV. 



