STAINING PRINCIPLES. 91 



(a) Fixation on Ordinary Slides. Gullantfs 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 a needle and the slide withdrawn.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 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 last. 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, side smeared 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. 



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. The sections are now ready to be stained. To save 

 repetition we shall in treating of stains suppose that, with 

 paraffin sections, these preliminary steps have already been 

 taken, and further that sections cut by a freezing microtome 

 are also in spirit and water. 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 (v. infra} and water, and- then wash- 

 ing in water containing a few drops of ammonia and finally 

 in pure water. 



Staining Principles. To speak generally, the protoplasm 

 of bacteria reacts to stains in a manner similar to the 



