STAINING OF SPORES. 103 



Leprosy bacilli are stained in the same way, but are 

 rather more easily decolorised than tubercle bacilli, and 

 it is better to use only 5 per cent sulphuric acid in 

 decolorising. 



In the case of specimens stained either by the original 

 Ziehl-Neelsen method, or by Fraenkel's modification, the 

 tubercle or leprosy bacilli ought to be bright-red, and the 

 tissue blue or brown, according to the contrast stain used. 

 Other bacteria which may be present are also coloured 

 with the contrast stain. 



Staining of Spores. If bacilli containing spores are 

 stained with a watery solution of a basic aniline dye the 

 spores remain unstained. The spores either take up the 

 stain less readily than the protoplasm of the bacilli or 

 they have a resisting envelope which prevents the stain 

 penetrating to the protoplasm. Like the tubercle bacilli, 

 when once stained they retain the colour with considerable 

 tenacity. The following is the method for staining 

 spores : 



1. Stain cover-glass films as for tubercle bacilli. 



2. Decolorise with i per cent sulphuric acid in water or with 

 methylated spirit. This removes the stain from the bacilli. 



3. Wash in water. 



4. Stain with saturated watery methylene-blue for half a minute. 



5. Wash in water, dry, and mount in balsam. 



The result is that the spores are stained red, the protoplasm of the 

 bacilli blue. 



The spores of some organisms lose the stain more readily than those 

 of others, and for some, methylated spirit is a sufficiently strong de- 

 colorising agent for use. If sulphuric acid stronger than I per cent is 

 used the spores of many bacilli are readily decolorised. 



Moller recommends that before being stained the films should be 

 placed in chloroform for 2 minutes, and then in a 5 per cent solution 

 of chromic acid for ^-2 minutes. This procedure has an advantage in 

 some cases, though in many it is unnecessary. 



The Staining of Flagella. The staining of the flagella 

 of bacteria is the most difficult of all bacteriological 

 procedures, and it requires considerable practice to ensure 

 that good results shall be obtained. Many methods have 



