96 GENERAL MICROBIOLOGY 



experiments show that so long as the Gram-stained cell 

 is intact, the solvent is unable to remove the stain, but 

 that as soon as the cell is crushed and injured, the stain 

 is, in great part, dissolved out. The amorphous debris 

 obtained from broken-up Gram-positive bacteria does not 

 retain Gram's stain. 



Apparatus. Clean slides; clean cover-glasses; plati- 

 num loop and needle; cover-glass forceps; distilled water; 

 anilin- water gentian violet; Lugol's iodin solution; aceton- 

 alcohol. 



Culture. Agar slant cultures preferably. 



Method. 1. Prepare a cover-slip film and fix in the 

 usual way. 



2. Stain in anilin-water gentian violet three to five 

 minutes. 



3. Wash in water. 



4. Treat with Lugol's iodin solution until the film is 

 black or dark brown. 



5. Wash in water. 



6. Dry in air. 



7. Wash in aceton-alcohol until no more color is dis- 

 charged. 



8. Wash in water. (Counterstain at this point if desired.) 



9. Dry in air. 



10. Mount in Canada balsam. 



Note. The Gram-Weigert method is more applicable in case of 

 sections of tissues. The directions from 1-6 are the same. The speci- 

 men is washed in anilin oil 1 part, xylol 2 parts, instead of alcohol, 

 washed further in xylol and mounted at once in Canada balsam. Bad. 

 bidgaricum in milk is very beautifully demonstrated by this modified 

 method. 



A few of the more common Gram-positive and -negative 

 organisms are appended. This is not as important a diag- 

 nostic method as has been formerly supposed, because 

 the reaction occurring often depends upon the age of the 

 culture, the medium on which it is grown, etc. 



