96 A MANUAL OF BACTERIOLOGY 



so as to form an emulsion, which is then spread over the 

 surface. As a general rule the material should be well 

 emulsified, but in some instances this is inadvisable, as a 

 particular formation or characteristic grouping may be 

 disturbed thereby, in which case, after a slight admixture 

 with the water, the emulsion is gently spread. The thin 

 moist film is allowed to dry, or may be dried by gentle 

 warming over the Bunsen flame, preferably holding the 

 preparation in the fingers and moving backwards and 

 forwards over the flame. The film, when dry, must next 

 be fixed, which is accomplished by passing the slide, 

 film side up, six times through the Bunsen flame (a cover- 

 glass is held in the forceps and passed three times through 

 the flame). Films may also be fixed in alcohol and ether 

 (p. 97). The object of this " fixing " is to thoroughly 

 dry the film and coagulate albuminous material, whereby 

 the film adheres better to the glass, and is not so likely 

 to be detached in the subsequent processes of staining 

 and washing, etc. Fixing may also tend to diminish the 

 staining capacity of the extraneous matter mixed with 

 the organisms. The preparations are now ready for 

 staining. 



When the culture is in a fluid medium, such as broth, 

 the tube is manipulated in the same way, the deposit at 

 the bottom having been shaken up if necessary, and a 

 loopful or two of the fluid removed with a looped platinum 

 needle, transferred to the glass, spread, dried, and fixed 

 as before, but as the medium is fluid there is usually no 

 need to add any water. 



If a specimen of blood, pus, or sputum is required, the 

 procedure is much the same. A little of the material is 

 taken up with a looped platinum needle and spread in a 

 thin film over the slide or cover- glass, which is then dried 

 and fixed, as described above. If necessary, a droplet 

 of tap water or physiological salt solution may be used 



