10 GENERAL BACTERIOLOGY LESSON 



(/) Once more dry the film in the air and pass it 

 through the flame. 



(g) Now stain the specimen by floating it with the 

 film surface downwards on the staining solution. 



For Streptococcus pyogenes and Torula alba use 



fuchsine. 



For Bacillus filamentosus use methylene-blue. 

 For the Staphylococcus pyogenes aureus and Sarcina 

 lutea use gentian-violet. 



Leave the films in the stain for some time (two to 

 five minutes), then wash in water and dry between folds 

 of filter -paper ; clean the unsmeared surface, mount in 

 water, and examine under a high power and Oc. 4, 

 using no diaphragm, and the plane reflector. 1 



If the specimen is successful, float it off the slide, dry 

 it again, and mount it permanently in xylol balsam. 

 Examine it with a ^ in. oil immersion. 

 Make drawings. 



If the specimen is not sufficiently stained, place it once 

 more in the staining fluid, and proceed as above. 



If the specimen is oversfcained, it is better to prepare a 

 fresh one. Weak acetic acid (nnnr), however, may be used 

 to decolourise it. 



Micro-organisms vary greatly in regard to their affinity 

 for dyes, and, again, some dyes stain more quickly than 

 others. Thus* aqueous methylene-blue hardly ever over- 



1 Stained specimens should always be examined without a diaphragm, 

 with an Abbe* condenser and a plane reflector ; unstained specimens 

 with a narrow diaphragm and a concave reflector without an Abbe 

 condenser. 



