152 BACTERIOLOGY. 



This method is particularly useful in demonstrating 

 the capsule which is seen to surround some bacteria, 

 particularly the micrococcus lanceolatus of pneumonia. 



GLACIAL ACETIC ACID METHOD. Another method 

 which may be employed for demonstrating the presence 

 of the capsule surrounding certain organisms is to pre- 

 pare the cover-slips in the ordinary way, then cover the 

 layer of bacteria upon them with glacial acetic acid, 

 which is instantly poured off (not washed off in water), 

 and the aniline-water gentian-violet solution dropped 

 upon them; this is allowed to remain three or four 

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

 and lastly the slip is washed off in a solution of sodium 

 chloride. Usually this is of the strength of the ordinary 

 physiological salt-solution, viz., 0.6 to 0.7 per cent., but 

 at times the strength must be greater, sometimes in- 

 creased to from 1.5 to 2 per cent, of salt. 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. 



STAINING OF SPORES. We have 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 very 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 



