158 THE MICROSCOPE. 



take place, which may be assisted by the application 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 water 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 consists of silica, will con- 

 tain all the infusorial forms ; and some of this may be taken up by a 

 fishing-tube, laid on a slide, and examined in the usual manner. Should 

 perfect specimens of the Coscinodiscus, Gallionella, or Navicula 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 ; or, if good, after being dried, may be 

 mounted in Canada balsam. 



Dr. Redfern has given us an excellent mode of isolating Naviculse 

 and other test- objects. He says : Having found the methods ordinarily 

 employed very tedious, and frequently destructive of the specimens, I 

 adopted the following 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 through a slit in a 

 piece of cork, use it as a forceps under a two-thirds of an inch objec- 

 tive, with an erecting eye-piece. When the split extremity of the hair 

 touches the glass-slide, its parts separate from each other to an amount 

 proportionate to the pressure, and on being brought up to the object, 

 are easily made to seize it, when it can be transferred as a single spe- 

 cimen to another slide without injury. The object is most easily 

 seized when pushed to the edge of the fluid on the slide. Hairs split 

 at the extremity may always be found in a shaving-brush which has 

 been in use for some time. Those should be selected which have thin 

 split portions so closely in contact that they appear single until touched 

 at their ends. I have also found entire hairs very useful, when set in 

 needle-holders, in a similar manner ; any amount of flexibility being 

 given to them by regulating the length of the part of the hair in use. 



We now proceed to notice in detail some of the most interesting of 

 the fossil Infusoria. 



Professor J. W. Bailey, of New York, has enriched the Museum of 

 the College of Surgeons with several valuable specimens of the skele- 

 tons of Infusoria ; among them is a fresh-water Bacillaria, named 



