254 H. J. CONN 



unless it has been carefully separated from its slime, the organisms 

 remaining unstained in a completely staiaed field. With rose 

 bengal, on the other hand, the organisms stain deeply, showing 

 their characteristic granules, and the field is practically unstained 

 even though the organisms have been growing on a medium 

 specially adapted to the production of slime. Ps. caudatus, 

 which is onh^ about 0.2 micron in diameter (see Conn and Bright, 

 1919), shows a peculiar and t3'pical granulation with this stain 

 that had not been suspected after considerable study with other 

 dyes. Rose bengal, indeed, seems to be unusually well adapted 

 for revealing structure in small bacterial cells. The very satis- 

 factory results obtained wdth it in this laboratory make it seem 

 worth recommending to bacteriologists in general. Although 

 more expensive than the more commonly used dj^es, its price 

 is not prohibitive unless an unusual amount of staining is to 

 be done. 



REFERENCES 



Conn, H. J. 1918 The microscopic study of bacteria and fungi in soil. N. Y. 



Agr. Exp. Sta., Tech. Bui. 64. 

 Conn, H. J., and Bright, J. W. 1919 Ammonification of manure in soil. J. 



Agr. Res., 16, 313-350. Also in N. Y. Agr. Exp. Sta., Tech. Bui. 67. 



