202 CLINICAL BACTERIOLOGY AND HiEMATOLOGY 



the other end of the slide with a steady uniform movement, and 

 in doing so the drop of blood is spread out into a long uniform 

 film. In this way a film ^ inch wide and 2 inches long can be 

 made on a single slide. A fresh piece of paper is to be used for 

 each specimen (see Fig. 52). 



The author is of opinion that it is best to adopt the cover-glass 

 method, as he has found that it presents fewer difficulties for 

 beginners ; this is not the universal experience, and it is a. good 

 plan to try both, and adopt that with which you get the best 

 results. 



Films are sometimes spread on one slide by means of another, 

 which is used as a spreader in much the same way as the 

 cigarette-paper described above. This is very good for malaria 

 parasites, and for alterations in the red corpuscles, but is useless 

 for making differential counts, as some of the leucocytes are 

 carried along with the spreader and left at the end of the film. 



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, though it answers 

 very well in skilful hands. Three methods should be learnt : the 

 method by heat, the alcohol and ether method, and the formalin 

 method. 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 Jennef's 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 practitioners, 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. — SUdes 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. 5), 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 



