STAINING OF SPORES. 183 



minutes, is poured off, and a few drops more are added, 

 and lastly the slip is washed in a solution of sodium 

 chloride. Usually this is of the strength of physio- 

 logical salt-solution, viz., 0.6 to 0.7 per cent. ; but at 

 times it must be stronger, occasionally as concen- 

 trated as 1.5 to 2 per cent. The reason for this 

 is that if the slips be washed in water, or in salt- 

 solution that is too weak, the mucin capsule that 

 has been coagulated by the acetic acid is redissolved 

 and rendered invisible. This does not occur when the 

 salt-solution is of the proper strength a point that can 

 be determined only after a few trials with solutions of 

 different strengths. (Welch.) A very clear, sharply cut 

 picture usually follows this method of procedure. 



Ribbert also recommends for the staining of capsu- 

 lated bacteria the momentary immersion of the cover- 

 slips in a saturated solution of dahlia in a mixture of 

 100 parts of water, 50 parts of alcohol, and 12^ parts 

 of glacial acetic acid ; after which the excess of color 

 is removed by washing in wajter^.vv^' 



STAINING OF SPORES. We*^*ce learned that one of 

 the points by which spores may be recognized is their 

 refusal to take up staining-substances when applied in 

 the ordinary way. They may, however, be stained by 

 special methods ; of these, one that has given fairly satis- 

 factory results in our hands is as follows : the cover- 

 slip is to be prepared from the material containing the 

 spores in the ordinary way, dried, and fixed. It is then 

 to be held by its edge with forceps, and its surface cov- 

 ered with Loftier' s alkaline methylene-blue solution. It 

 is then held over the Bunsen flame until the fluid boils ; 

 it is then removed, and after a few seconds is heated 

 again. This is continued for about one minute, after 

 which it is washed in water and then decolorized in 



