8 CHAPTER I. 



8. Preparation of Entire Objects, or of Material that is not to 

 be sectioned. The treatment of objects which can be studied 

 without being cut into sections is identical with that above 

 described, with the omission of those passages that relate to 

 imbedding processes. Its normal course may be described 

 as fixation, washing out, staining, treatment with successive 

 alcohols of gradually increasing strength, final dehydration 

 with absolute alcohol, clearing, and mounting in balsam. 



In the preparation of entire objects or structures that 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 described ( 5). Fluids of high diffusibility should be 

 employed as far as possible in all the processes. Fixing 

 agents of great penetrating power (such as picric acid or 

 alcoholic sublimate solution) should be employed where the 

 objects present a not easily permeable integument. Wash- 

 ing 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 to be recom- 

 mended are Grenadier's boi*ax-carmine, or one of Mayer's 

 alcoholic carminic acid or haematein stains. Aqueous stains 

 are more rarely indicated, though there are many cases in 

 which they are admissible, and some in which they are 

 preferable. 



9. Minute Dissections. These are best done, if necessary, in a 

 drop of clearing agent. I recommend cedar-wood oil for 

 tin's purpose, as it gives to the tissues a consistency very 

 favourable for dissection, whilst its viscosity serves to lend 

 <upport to delicate structures. Clove oil lias a tendency !<> 

 make tissues I lint lisive lain in it for some time very brittle. 



