PREPARATION OF SECTIONS FOR STAINING. 95 



temperature 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. (#) Gulland"*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 slide withdrawn.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 with- 

 stand all the manipulations necessary during staining and mounting. 



(ti) 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 of the slide 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 stain- 

 ing, 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. These can be readily removed by placing 

 the sections, before staining, for a few minutes in equal parts of 

 Gram's iodine solution (p. 102) and water, and then washing out 

 the iodine with methylated spirit. 



To save repetition we shall in treating of stains suppose that, 

 with paraffin sections, the above preliminary steps have already 

 been taken, and further, that sections cut by a freezing micro- 

 tome are also in spirit and water. 



