216 HISTOLOGICAL PREPARATIONS 



to stand, then filter through filter paper and add an equal volume of glycerin 

 to the clear filtrate. Add a little piece of camphor or thymol as a preserva- 

 tive and keep in a well-stoppered bottle. Before using the solution shake the 

 bottle well to ensure the mixture being homogeneous. 



Method of use. Place a drop of the albumin on the slide and spread it in 

 a very thin layer with the tip of the index finger. Transfer the section with 

 a spatula direct to the prepared slide, carefully spread it out with a fine 

 brush so that there are no folds and press it lightly to make it adhere to 

 the albumin. 



Should there be any difficulty in getting the sections to spread, a drop of water 

 may be placed on the slide already smeared with the albumin mixture and the 

 section laid on the drop of water. The slide is then gently heated on the drying 

 stage (fig. 127, p. 141) until the section has spread evenly, the excess of water is 

 then taken up with a piece of silk paper and the process continued as below. 



Heat the under side of the slide very lightly over the pilot flame of a Bunsen 

 and in a few seconds the section will have adhered to the surface of the glass. 

 The section is now treated with xylol and then with absolute alcohol to 

 remove the paraffin, after which it is ready for staining. 



Note. The albumin-fixation method has the disadvantage of not being universally 

 applicable: it cannot, for instance, be used with alkaline solutions, Orth's picro- 

 carmine, etc., -which dissolve albumin. 



5. The staining 1 of sections. 



In order to render the detection of micro-organisms as easy as possible and 

 to facilitate their study, it is desirable that they should be stained a different 

 colour from the tissue in which they are contained ; hence it is best to use 

 either a double or triple staining method. Unfortunately such methods are 

 of little use when dealing with an organism which is gram-negative and 

 which does not stain either by Ehrlich's or Ziehl-Neelsen's method. In 

 such a case it is sometimes not possible to differentiate further than by staining 

 with a simple stain in such a way that the background (the animal tissue) is 

 only lightly stained while the bacteria (the vegetable tissue) are stained much 

 more deeply. Recently, however, methods of double staining applicable to 

 gram-negative organisms have been devised and two of these will be described. 



The description of Ehrlich's and Ziehl-Neelsen's methods will be deferred 

 to the chapter on tuberculosis. 



A. Simple staining. 



Methods applicable to most organisms. 



(a) Weigert's method. 1. Cover the section with a few drops of aniline- 

 gentian-violet (p. 139). Allow the stain to act for 30 minutes or so and then 

 blot up the excess. 



2. Immerse the section for a few seconds in a vessel containing a 0'5 per 

 cent, aqueous solution of acetic acid. 



3. Wash carefully in distilled water and blot up the excess. 



4. Dehydrate very rapidly in absolute alcohol. 



5. Clear in clove oil then in xylol. 



6. Mount in Canada balsam. 



(ft) Loeffler's method. The stains used are Loeffler's alkaline blue (p. 139) 

 (15 minutes) or Ziehl's fuchsin (p. 138) (5 or 6 minutes). The technique is 

 otherwise the same as in the preceding method. 



(7) Kiihne's method A. 1. Stain for 15 minutes in carbol-blue or 

 ammoniacal blue (pp. 138 and 139). 



2. Transfer to distilled water. 



