258 CLINICAL. BACTERIOLOGY AND H^MATOLOGY 



FIXATION OF BLOOD-FILMS. 



, If films are required simply for bacteriological purposes 

 (i.e., to search them for bacteria), they may be fixed by passing 

 them three times through the flame, just as if they were 

 ordinary films. This, however, is not to be recommended in 

 the study of the cells of the blood or of the parasite of malaria, 

 thoug'h it answers very well in skilful hands. Four methods 

 should be learnt : heat, alcohol and ether, perchloride, and 

 formalin. Of these, the first is necessary if Ehrlich's triacid 

 stain is to be used, but the others are perhaps better for other 

 stains. In addition to these we must mention that if Jennets 

 stain is used a preliminary fixation is unnecessary, as the fluid 

 fixes the film and stains it at the same time. This is the 

 method of blood examination which is most suitable for prac- 

 titioners, and it is doubtful whether it is not also the best for 

 the most accurate and delicate scientific research. 



I. Method of Fixation by Heat. Slides or cover-glasses to 

 be fixed by this method must be exposed to a temperature of 

 120 C. for about five minutes slides requiring a slightly 

 longer time than cover-glasses. 



The ideal way is to use a dry-air sterilizer (see p. 3), to place 

 the films in it whilst cold, to heat up to 120 C., and then to 

 turn out the gas. In the absence of this apparatus a metal 

 slab or plate such as has been recommended for use in staining 

 the tubercle bacillus answers well. It is mounted upon a 

 tripod stand, and the heat applied at one end. After a time 

 the temperature of various portions of the plate is tested by 

 the application of a few drops of water; the point at which the 

 drop assumes the " spheroidal state " (i.e., takes the form of a 

 sphere, and does not wet the plate) is about the right point to 

 use. The slides or films are placed at this point for the appro- 

 priate time. 



II. Fixation by Perchloride of Mercury. Flood the film 

 with a saturated watery solution of perchloride of mercury, 

 allow to act for a minute, and wash for a minute under the 

 tap, or by washing it in a vessel of water. 



This method of fixation is, perhaps, the best that can be 

 used for general purposes. 



III. Fixation by Alcohol and Ether. This is very simple; 



