4 INTRODUCTORY. 



clearing agent if a good clearing agent be employed. Oil of cedar 

 will remove the remaining water from tissues saturated with 95 per 

 cent, alcohol ; oil of bergamot will " clear " from 90 per cent, 

 alcohol, and anilin oil will clear from 70 per cent, alcohol. 



I am not aware of any substance that can entirely take the place 

 of alcohol for dehydration and preservation. Acetone and methylal 

 have been substituted for alcohol in the dehydration of methylen- 

 blue preparations (PARKER, Zool. Anz., 403, 1892, p. 376), and 

 anilin oil can be made to dehydrate watery sections if they be first 

 mopped up with blotting-paper ; but a really efficient substitute for 

 alcohol in general work remains yet to be discovered. 



4. Preservation. Considered as a mere dehydrating agent, 

 alcohol fulfils its functions fairly well. But considered as a histo- 

 logical preservative agent, it is far less satisfactory. If tissues be 

 left in alcohol for only a few days before further preparation, injurious 

 effects will perhaps not be very disagreeably evident. But it is 

 otherwise if they are put away in it for many weeks or months before 

 the final preparation is carried out. The dehydrating action of the 

 alcohol being continuously prolonged, the minute structure of 

 tissues is 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. 

 wiss. Mik., 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 (Arch. mik. Anat., 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 recom- 

 mend 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 paraffin. 

 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 preservation of the tissues is concerned, but of course it is 

 not so handy for storage. 



