PREPARATION OP FOSSIL INFUSOKIA. 435 



on further details of the fossil Infusoria, we would first 

 state how they may be prepared for microscopic examina- 

 tion. A great many of the infusorial earths may be 

 mounted as objects without any previous washing or pre- 

 paration ; some, such as chalk, however, must be repeat- 

 edly washed, to deprive the Infusoria of all impurities ; 

 whilst others, by far the most numerous class, require 

 either to be digested for a long time, or even boiled in 

 strong nitric or hydro-chloric acid, for the same purpose. 

 Place a small portion of the earth to be prepared in a test- 

 tube, or other convenient vessel, capable of bearing the 

 heat of a lamp ; then pour upon it enough diluted hydro- 

 chloric acid to about half fill the tube. Brisk effervescence 

 will now take place, which may be assisted by the applica- 

 tion of a small amount of heat, either from a sand-bath or 

 from a lamp : as soon as the action of the acid has ceased, 

 another supply may be added, and the same continued 

 until no further effect is produced. Strong nitric acid 

 should now be substituted for the hydro-chloric, when a 

 further effervescence will take place, which may be greatly 

 aided by heat ; after two or three fresh supplies of this 

 acid, distilled w.ter may be employed to neutralise all the 

 remains of the acid in the tube ; and this repeated until 

 the water comes away perfectly clear, and without any 

 trace of acidity. The residuum of the earth, which con- 

 sists of silica, will contain all the infusorial forms ; and 

 some of this may be taken up by a dipping-tube, laid on 

 a slide, and examined in the usual manner. Should per- 

 fect specimens of the Coscinodiscus, Gallionella, or Navi- 

 cula be present, they may be mounted in Canada balsam ; 

 if not, the slide may be wiped clean, and another portion 

 of the sediment taken, and dealt with in the same way, 

 which, if good, after being dried, may be mounted in Canada 

 balsam. 



Dr. Redfern adopts an excellent mode of isolating Navi- 

 culce and other test-objects. He says : " Having found 

 the methods ordinarily employed very tedious, and fre- 

 quently destructive of the specimens, I adopted the follow- 

 ing plan. Select a fine hair which has been split at its 

 free extremity into from three to five or six parts, and 

 having fixed it in a common needle-holder by passing it 



