DEHYDRATION AND CLEARING 97 



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) 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 needle and the slide withdrawn.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 down- 

 wards, 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 manipulations 

 necessary during staining and mounting. 



(6) 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 down- 

 wards, 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 

 corresponding 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 removed by placing the 

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

 Gram's iodine solution (p. 103) 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 microtome 

 are also in spirit and water. 



Dehydration and Clearing. — It is convenient, first of all, to 

 indicate the final steps to be taken after a specimen is stained. 

 Dry films after being stained are washed in water, dried and 



