10 JOURNAL OF THE [January, 



The well-dried bacteria films are immersed half an hour (or, if 

 need be, five minutes at 60° C.) in the 



Fixing Bath. 



Osmic acid (2 percent solution) i part. 



Tannin (10- to 25-per-cent solution) 2 parts. 



They are then washed with utmost care in water and in alcohol, 

 and placed a few seconds in the 



Sensitizing Bath. 

 Silver nitrate, a very weak solution (0.5 to 0.25 percent). 

 Without washing, they are next subjected to the action of the 



Reducing Bath. 



Gallic acid 5 parts. 



Tannin 3 " 



Melted sodium acetate 10 " 



Distilled water 350 ' ' 



After a few moments they are returned to the silver bath, re- 

 ;moved when the bath begins to blacken, washed thoroughly, 

 dried, and mounted in balsam. 



I have made trial, with some success, of this promising method, 

 in reference to the more general object of the present paper. So 

 far I find an objectionable tendency to blackening and over- 

 staining of the whole preparation, which I think may be obviated 

 by reducing the strength of the baths. 



The successful results already obtained in direct staining of 

 living bacteria by simple processes, like those of Sjobring, Straus, 

 Klein, and Maddox, warrant the prophecy that some such pro- 

 cess, with or without application of mordant, as tested on each 

 kind, will yet come into general use when the utmost perfection 

 is desired in a preparation. In other cases such staining of 

 living bacteria may well precede their drying on covers in the 

 ordinary way, when the containing liquid is sufficiently free from 

 substances inclined to absorb the stain. 



Preparations of Spirilla. — In regard to spirochgete, spirillum, 

 and vibrio forms, the preliminary process of killing with a fixa- 

 tive, before evaporation of the film, was found to have materially 



