SIMPLE STAINING OF FILMS 205 



2. Fixation. Several methods are available for fixing films on slides and 

 cover-glasses. 



(a) Heat. The slide or cover-glass with the film upwards is held in a 

 pair of Cornet's forceps (fig. 118, p. 131) and passed three times through the 

 heating flame of a Bunsen burner or spirit lamp. The shape of the cells is 

 somewhat distorted by this procedure and it cannot therefore be used (for 

 example) for fixing blood-films. 



(/3) Alcohol-ether. Pour two or three drops of alcohol-ether on the cover- 

 glass (p. 141) and allow it to dry in the air. This method is preferable to the 

 preceding as it preserves absolutely the shape of the cells. It is occasionally 

 necessary to allow the solution to act for several minutes. 



(7) Absolute alcohol. In many cases absolute alcohol can be used in place 

 of alcohol-ether for fixing films. The technique is the same as that described 

 in the preceding paragraph. With many dyes staining is facilitated by 

 allowing the alcohol to act for 10-30 minutes. 



(S) Other solutions are occasionally used for fixing films, e.g. osmic acid 

 vapour, absolute methyl alcohol, etc. These will be referred to when 

 occasion for their use arises. 



(b) Scrapings of organs. 



Films of the internal organs are prepared as follows : 



1. Transfer to a slide with a platinum loop or pipette a small piece of tissue 

 from the organ, and spread it by rubbing it on the slide so as to cover a 

 rectangular area about 15-20 mm. square. Or a piece of the tissue (liver, 

 spleen, etc.) may be taken up in a pair of dissecting forceps and lightly 

 rubbed over the surface of the slide. 



The film in any case should be thin and uniform and any lumps which 

 would interfere with the application of a cover-glass must be removed. 



2. Dry as above. 



3. Fix by heat or with alcohol-ether. 



Films of the brain or spinal cord should always be washed several times in the 

 alcohol-ether mixture after fixing to remove fatty matters, as these would inter- 

 fere with the subsequent staining processes. 



(c) Sputum. 



When the sputum is fluid it can be treated as a fluid exudate, but should 

 it be tough or inspissated it should be spread with a platinum loop on a 

 slide ; it will facilitate the preparation of a thin and uniform film if the slide 

 be gently heated while the sputum is being spread. Dry and fix. 



B. Staining methods. 



Films whether of fluids or scrapings of organs contain structures of two 

 different kinds. 



1. The groundwork, which is formed of tissues of animal origin cells 

 and amorphous elements. 



2. Bacteria, which are of vegetable origin. 

 Such films may be stained in one of two ways, 



(a) With a simple stain by which at a single operation the groundwork and 

 the micro-organisms are stained the same colour. 



(b) With a double slain by means of which the micro-organisms are 

 differentiated from the groundwork by being stained a different colour. 



(a) Simple staining. 



A blood film or a scraping of an organ may be stained with any of the dyes 

 described in Chapter VIII. 



