322 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



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 ifjenney'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.— -S\iAes 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 

 tubercle bacillus answers well. It is mounted upon a tripod 

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

 perature 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 appropriate 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; the 

 films are placed in a mixture of equal parts of alcohol and ether 

 for at least half an hour. 



This method of fixation is good, but slow. 



