136 The Microscope. 



large size may be satisfactorily stained with it. I consider it desir- 

 able to supplement this staining with an additional eosine stain. 

 For this purpose, after the parts have been stained in alum cochineal, 

 they are left to soak in water for half an hour or so ; if this is not 

 done, the subsequent use of alcohol will produ^ce alum crystals in 

 the interior of the tissues, and interfere with the cutting very ser- 

 iously. After washing, the object is placed in an alcoholic solution of 

 O.b^ of eosine and left over night, or in case of large objects even 

 longer. For some tissues this staining is too intense, and it is nec- 

 essary to put the object subsequently into alcohol to extract a 

 portion of the color, at least from the outer part of the object, 

 which may be over-stained, while the inner parts are not stained 

 quite enough. By the second treatment with alcohol the over- stain- 

 ing is corrected easily; experience teaches one very soon the exact 

 amount of washing out or extraction which each sort of tissue 

 requires. When the nuclei are stained with logwood instead of 

 with cochineal, the result is preferable, but logwood cannot be used 

 except for small objects. Very good results may be reached with 

 Beale's carmine, also with borax carmine, and it seems not improb- 

 able that safranine might be advantageously employed. Of course 

 for special purposes, special methods of staining must be selected, 

 according to the object. For general work, however, I regard stain- 

 ing with alum cochineal and eosine as the best I have tried. After 

 the sections are cut, I find it best to arrange them at once in proper 

 serial order on a sheet of paper; they may then be left in any place 

 moderately warm and protected from dust, until it is convenient to 

 mount them. For actual mounting I employ a method, which, in the 

 precise form I have adopted, has not yet been described any where ; 

 the material for fastening the sections is celloidine or gun cotton, 

 dissolved in acetone. The use of acetone as a solvent was suggested, 

 I think, first by Altmann. It is desirable to use pure acetone ; the 

 ordinary commercial acetone is hardly good enough, but one can 

 get pretty fair results with it. The solution is spread over the glass 

 slide with a brush, and the slide held in a sloping position so that 

 as much of the fluid as possible will run off ; when the coat is dry 

 it should be almost perfectly transparent, and if there is any decided 

 cloudiness or milky look about it, the solution is too thick and must 

 be diluted with an addition of acetone, which must be carried so far 

 that a coat on the glass slide ^^can be obtained from it of the requi- 

 site transparency. When the celloidine upon the slide is thoroughly 

 hardened, the sections in parafiine are laid out upon it in the desired 

 order, then with the finger the band of sections are rolled. It will 



