112 A MANUAL OF BACTERIOLOGY 



fixed in alcohol and ether (p. 113). 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 sub- 

 sequent processes of staining and washing, etc. Fixing 

 may also tend to diminish the staining capacity of the 

 extraneous matter mixed with the organisms. The pre- 

 parations are now ready for staining. 



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

 a loopful or two of the fluid are removed with a looped 

 platinum needle, the deposit at the bottom having been 

 shaken up if necessary, transferred to the slide, spread, 

 dried, and fixed as before, but as the medium is fluid 

 there is usually no need to add any water. With a stab- 

 culture, a looped needle should be used to remove the 

 growth. 



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 

 to dilute the material so as to obtain a thinner film. If a 

 specimen is to be made from an organ, a particle of the 

 pulp is picked up and an emulsion made as before, or a 

 small piece of the organ may be held in sterile forceps and 

 the cut surface gently smeared over the slide or cover- 

 glass, which is then similarly dried and fixed ; these are 

 termed " smear preparations." 



Another method is to place a particle of the material 

 on a slide, apply over it a second slide, and by crushing 

 and rubbing the material between the two slides, and 

 finally drawing them apart, a film is formed on both 

 slides. 



Fixation. To obtain the best results it is preferable 



