INTRODUCTORY 6 



some hours in clean xylol, and pass through alcohol into the new stain. 

 This succeeded in every case with series of sections mounted on Mayer's 

 albumen, or by the water method. For shellac-mounted series, see 

 E. Meyer, Biol. Centralb., x, 1890, p. 509, or 7tli edition. 



The most convenient vessels in which to perform the various operations 

 of staining, differentiating, dehydrating, clearing, etc., on the slide, 

 are flat-bottomed corked glass tubes. Lee uses tubes 10 cm. high and 

 27 nmi. internal diameter. Each of these will then take two slides, 

 English size, placed back to back. 



6. Resume of the General Method. To sum up, you may 

 either fix, wash out, stain, wash, dehydrate, clear, imbed, cut 

 sections, clear and mount them in balsam ; or fix, wash, dehy- 

 drate, clear, imbed, cut, stain, wash, dehydrate, clear and mount 

 — according to choice. (See § 1424.) 



7. 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 oinission 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 endosinosis 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 

 lluids may mingle without hindrance. And in all cases the passage 

 is made gradual by placing the clearing medium under the alcohol, 

 as described (§ 4). Fluids of high diffusibility should be employed 

 as far as possible in all the processes. Fixing agents of great 

 penetrating power (each as picric acid or alcoholic sublimate 

 solution) should be employed where the objects present a not 

 easily permeable integument. Washing out is done with succes- 

 sive 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 pre- 

 ference with alcoholic staining media. The stains most to be 

 recommended are Grenadier's borax-carmine, or one of Mayer's 

 alcoholic carminic acid or hsematein stains. Aqueous stains are 

 more rarely indicated, though there are many cases in which 

 they are admissible, and some in which they are preferable. 



8. Minute Dissections. These are best done, if necessary, in 

 a drop of clearing agent. Lee recommends cedar-wood oil for 

 this purpose as it gives to the tissues a consistency very favourable 



