INTRODUCTORY. 5 



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 inethylal have been 

 substituted for alcohol in the dehydration of methylen-blue preparations 

 (PARKER, ZooL Anz., 403, 1892, p. 376) ; but a really efficient substitute 

 for alcohol in general work remains yet to be discovered. Formaldehyde 

 (see under Fixing and Hardening Agents) is now known to be a most 

 admirable medium for the preservation of museum specimens, being for that 

 purpose in many cases greatly superior to alcohol ; but experience is want- 

 ing as to how far it is available for the preservation of histological material, 

 whilst of course, occurring as it does in the form of an aqueous solution, it 

 can have no dehydrating effect. 



Considered as a mere dehydrating agent, alcohol fulfils 

 its functions fairly well. But considered as a histological 

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

 left in alcohol for only a few days before further prepara- 

 tion, the injurious effects of a sojourn in alcohol 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. KDLTSCHITZKY (Zeit. f. rviss. Mik., iv, 3, 1887, 

 p. 349) has proposed to remed} 7 this by putting up objects, 

 after fixation and washing out with alcohol, in ether, xylol, 

 or toluol. FI.EMMING (Arch. f. milt. 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 stnining power much 

 better. After extensive experience of this plan I can highly 

 recommend it, and would only further suggest that the action 

 of the liquid seems to me to be in many cases much im- 

 proved by addition of a little acetic acid (say 0'5 to 0*75 

 per cent.). 



