20 *$ GENERAL BACTERIOLOGY LESSON 



(c) Place the films in 20 per cent acetic acid for three to 

 five minutes. 



(d) Wash them in water, dry them between folds of 

 blotting-paper, and pass them again through the flame. The 

 films are now ready for staining. 



(1) Lqffler's methylene-blue. 



(a) Place one film in the stain for two to five minutes. 



(b) Wash in water, dry and mount in xylol balsam. 



Examine with ^ in. oil immersion : observe the 

 leucocytes and cocci (Staphylococci or Streptococci, 

 or both ; many probably in the leucocytes). 



(2) Gram's method. 



(a) Place the other film in absolute alcohol for one to 

 two minutes. 



(b) Stain it in aniline gentian-violet for one to two minutes. 



(c) Remove the superfluous stain with blotting-paper. 



(d) Now place in Gram's solution of iodine for half a 

 minute, until the specimen turns black. 



(e) Soak up the superfluous iodine solution. 



(/) Wash in alcohol till the film is almost colourless. 



(g) Pass quickly through a diluted alcoholic solution of 

 cosine, which stains the leucocytes and ground substance 

 pink. 



(h) Wash in water, dry and mount in xylol balsam. 



Examine with a high power, and then with -fa m - ^ 

 immersion : the pus cocci are stained dark violet, 

 and also the chromatine of the nuclei ; the ground 

 substance and protoplasm of the leucocytes are pink. 



