A NEW MODIFICATION AND APPLICATION OF THE 



GRAM STAIN 



G. J. HUCKER 



New York Agricultural Experiment Station, Geneva, New York 



Received for publication December 12, 1920 



In making microscopical examinations of the quality of milk 

 received at New York state cheese factories a need arose for a 

 stain which would have a greater differential value than methy- 

 lene blue, and which would be applicable for quantitative as well 

 as qualitative results. The thought of the Gram stain at once 

 suggested itself. While organisms can be classified only into 

 general groups in methylene blue preparations, and no differen- 

 tiation can be made between desirable and undesirable types for 

 cheese making, the gas forming groups can be readily distin- 

 guished from the desirable lactic acid organisms in slides stained 

 by the Gram method. 



In developing a modification of the Gram stain which could be 

 used in staining milk smears, the difficulty has been to secure a 

 decolorizing solution which would allow the Gram positive organ- 

 isms to retain the stain and still remove the color from the milk 

 and the Gram negative types. The following method has proved 

 satisfactory in our work, and is presented with the hope that it 

 will help solve similar difficulties for other investigators. 



The stain is as follows: 



Gentian violet solution 



Anilin oil 3.0 cc. 



Alcohol (absolute) 7.0 cc. 



Water 90.0 cc. 



Shake; filter 



Gentian violet (Griibler) 2.0 grams 



Iodine solution 



Iodine 1.0 gram 



Potas.sium iodide 2.0 grams 



Water 300. cc. 



395 



