102 MICROSCOPIC METHODS. 



needle with a rectangle of stiff writing paper fixed on it as 

 in the diagram (Fig. 39). When cut, sections are floated 

 on the surface of a beaker of water kept at a tempera- 

 ture about 10 C. below the melting-point of the paraffin. 

 On the surface of the warm water they become perfectly 

 flat. 



Fixation on Ordinary Slides, (a) Gu Hand's Method. A supply of 

 slides well cleaned being at hand, one of them is thrust obliquely into 

 the water below the section, a corner of the section is fixed on it with 

 a needle and the slide withdrawn. The surplus of water being wiped 

 off with a cloth, the slide is placed on a support, with the section 

 downwards, and allowed to remain on the top of the paraffin oven or 

 in a bacteriological incubator for from twelve to twenty-four hours. It 

 will then be sufficiently fixed on the slide to withstand all the manipu- 

 lations necessary during staining and mounting. 



(b) Fixation by Mann's Method. This has the advantage of being 

 more rapid than the previous one. A solution of albumin is prepared 

 by mixing the white of a fresh egg with ten parts of distilled water and 

 filtering. Slides are made perfectly clean with alcohol. One is dipped 

 into the solution and its edge is then drawn over one surface of another 

 slide so as to leave on it a thin film of albumin. This is repeated with 

 the others. As each is thus coated, it is leant, with the film downwards, 

 on a ledge till dry and then the slides are stored in a wide stoppered 

 jar till needed. The floating out is performed as before. The 

 albuminised side is easily recognised by the fact that if it is breathed 

 on, the breath does not condense on it. The great advantage of this 

 method is that the section is fixed after twenty to thirty minutes' 

 drying at 37 C. If the tissue has been hardened in any of the 

 bichromate solutions and embedded in paraffin, this or some corre- 

 sponding method of fixing the sections on the slide must be used. 



Preparation of Paraffin Sections for Staining. Before 

 staining, the paraffin must be removed from the section. 

 This is best done by dropping on xylol out of a drop bottle. 

 When the paraffin is dissolved out, the superfluous xylol is 

 wiped off with a cloth and a little absolute alcohol dropped 

 on. When the xylol is removed the superfluous alcohol is 

 wiped off and a little 50 per cent methylated spirit dropped 

 on. During these procedures sections must on no account 

 be allowed to dry. The sections are now ready to be 

 stained. Deposits of crystals of corrosive sublimate often 

 occur in sections which have been fixed by this reagent. 



