50 EXAMINATION AND STAINING OF BACTERIA. 



per cent, solution of chromic acid, again washed in water, and 

 stained in hot Ziehl's carbol-fuchsin solution for five minutes. 

 The staining fluid is poured off and, without washing in water, 

 the preparation is decolorized in 5 per cent, sulphuric acid. 

 After this it is again washed in water, and finally stained for 

 two or three minutes in the watery methylene-blue solution. 



The spores will be stained red, the body of the cells blue. 



The action of the chloroform is to dissolve the fatty crys- 

 tals that may be in the preparation. The chromic acid acts 

 on the membrane of the spores and permits the entrance of 

 the stain. 



The Fourth Method (Fiocca's). 



Ten to 20 parts of an alkaline solution of an anilin color 

 are added to 20 c.c. of a 10 per cent, ammonia solution in a 

 watch-glass ; then heat is applied until steam commences to 

 be given off. The cover-glass stays in this hot solution from 

 three to five minutes ; it is then taken out and washed in a 

 20 per cent, solution of nitric or sulphuric acid to decolorize it, 

 then washed again, when a contrast-color may be given. 



It must be remembered that there is considerable difference in 

 the behavior of spores of different bacteria to the staining methods 

 described; some stain very readily and others with considerable 

 difficulty. 



Practice will be the best guide as to which method is best to 

 employ and to what extent it should be carried out. 



VII. The Staining of Flagella. 



The hair-like processes of the bacteria which serve for 

 their locomotion, the flagella, can not, on account of their 

 fineness, be seen in any stained specimen, nor can they be 

 stained by any of the ordinary methods just described for 

 staining bacteria. In order to make them visible, it is neces- 

 sary to use special stains in which the action of mordants plays 

 an essential part. 



1. Loeffler's Method. 



This is the most common method, and is as follows : Clean 

 very carefully a thin cover-glass, and spread very thinly and 



