INTRODUCTORY. 5 



sometimes considerably altered by it ; they become over-hard 

 and shrink, and become brittle, and their capacity for taking- 

 stains well becomes seriously diminished. KULTSCHITZKY 

 (Zeit. wins. Mik.j iv, 1887, p. 349) has proposed to remedy 

 this by putting up objects after fixation and washing out 

 with alcohol in ether, xylol, or toluol. FLEMMING (ArcJi. 

 mik. Anat.j xxxvii, 1891, p. 685) advises putting up objects 

 after fixation in a mixture of alcohol, glycerin, and water, 

 in about equal parts, pointing out that objects thus preserved 

 may be at any moment either prepared for sectioning by 

 treatment with pure alcohol or softened for dissection or 

 teasing by a little soaking in water, and that they do not 

 become so hard and brittle as alcohol specimens, and retain 

 their staining power much better. After extensive experience 

 of this plan I can recommend it, and would only further 

 suggest that the action of the liquid seems to me to be in 

 many cases much improved by addition of a little acetic acid 

 (say 0'5 to 0*75 per cent.). 



For material that is intended only for section-cutting, I 

 find that by far the best plan is to clear (next ) and imbed 

 at once in pa-raffin. This affords, as far as I can see, an 

 absolutely perfect preservation. Cedar-wood oil is, I find, 

 nearly, if not quite, as good as paraffin, so far as the preser- 

 vation of the tissues is concerned, but of course it is not so 

 handy for storage. 



5. Removal of Alcohol; Clearing.- -The water having been 

 sufficiently removed, as described in 3, the alcohol is in its 

 turn removed from the tissues, and its place taken by some 

 anhydrous substance, generally an essential oil, which is 

 miscible with the material used for imbedding or mounting. 

 This operation is generally known as Clearing. It is very 

 important that the passage from the last alcohol to the clear- 

 ing agent be made gradual. This is effected by placing the 

 clearing medium under the alcohol. A sufficient quantity 

 of alcohol is placed in a tube (a watch-glass will do, but 

 tubes are generally better), and then with a pipette a suffi- 

 cient quantity of clearing medium is introduced at the bottom 

 of the alcohol. Or you may first put the clearing medium 

 into the tube, and then carefully pour the alcohol on to the 

 top of it. The two fluids mingle but slowly. The objects 



