6 INTRODUCTORY. 



are intact and covered by an integument not easily permeable 

 by liquids, special care must be taken to avoid swelling from 

 endosmosis on the passage of the objects from any of the 

 liquids employed to a liquid of less density, or shrinkage from 

 exosmosis on the passage to a liquid of greater density. This 

 applies most specially to the passage from the last alcohol 

 into the clearing medium. A slit should be made in the 

 integument, if possible, so that the two fluids may mingle 

 without hindrance. And in all cases the passage is made 

 gradual by placing the clearing medium under the alcohol, as 

 above described. Fluids of high diffusibility should be em- 

 ployed as far as possible in all the processes. Fixing agents 

 of great penetrating power (such as picrosulphuric acid or 

 alcoholic sublimate solution) should be employed where the 

 objects present not a easily permeable integument. Washing 

 out is done with successive alcohols, water being used only in 

 the case of fixation by osmic acid, or the chromic mixtures or 

 other fixing solutions that render washing by water imperative. 

 Staining is done by preference with alcoholic staining media. 

 The stains most used are Grenadier's borax-carmine, Mayer's 

 modification of Grenadier's alcoholic carmine, and Kleinen- 

 berg's hsematoxylin (for all these see STAINING AGENTS). 

 Anilin stains are rarely applicable to this class of preparations. 

 Aqueous stains are more seldom used, though there are many 

 cases in which they are admissible, and some in which they 

 are preferable. 



Minute dissections are best done, if necessary, in a drop of 

 clearing agent. I recommend cedar- wood oil for this purpose, 

 as it gives to the tissues a consistency very favorable for dis- 

 section, whilst its viscosity serves to lend support to delicate 

 structures. Clove oil has a tendency to make tissues that 

 have lain in it for some time very brittle. This brittleness is 

 also sometimes very helpful in minute dissections. Another 

 property of clove oil is that it does not easily spread itself 

 over the surface of a slide, but has a tendency to form very 

 convex drops. This property also makes it frequently a very 

 convenient medium for making minute dissections in. 



5. Following Paul Mayer, I gave in the first edition the 

 following reasons for employing alcoholic rather limn aqueous 

 staining media. Since, in most cases, treatment with alcohol 



