ROSE BENGAL AS A GENERAL BACTERL^L STAIN 



H. J. CONN 

 New York Agricultural Experiment Station 



Received for publication October 2, 1920 



Recently the use of rose bengal was mentioned (Conn, 1918) 

 as a stain for detecting microorganisms in the soil. It has 

 subsequently been found to be especially useful in staining two 

 soil organisms, B. radicicola and Ps. caudatus, both of which are 

 hard to stain by ordinary methods on account of the slime they 

 produce. Its use with these two species proved so successful 

 that it is now one of the bacterial stains most commonly used in 

 this laboratory, and it almost always gives satisfaction. 



Rose bengal is a stain little known among bacteriologists, but 

 deserves wider use. It belongs to the phthalein series of dyes, 

 being closely related chemically to eosin. It differs from the 

 latter stain in that the four atoms of bromine in eosine are 

 replaced by four atoms of iodine with the addition of two atoms 

 of chlorine. The dye as formerly made in Germany was appar- 

 ently quite reliable, but it has scarcely ever been manufactured 

 in America and it has proved difficult to get a satisfactory product 

 of domestic manufacture. Some of the imported material is 

 still available, and after investigation an American-made product 

 has been found, sold by the Will Corporation as their "bioloid" 

 grade, which gives as good results as that of German manufacture. 

 The formula which has proved satisfactory is: Rose bengal, 1 

 gram; 5 per cent phenol, 100 cc. This solution remains in good 

 condition for several months. 



The chief value of this stain to the bacteriologist is that it 

 has a great affinity for bacterial protoplasm but not for the 

 slime or debris with which the cells are surrounded. It is there- 

 fore especially to be recommended for slime-formers. B. radici- 

 cola, for instance, does not take the ordinary bacterial stains 



253 



