152 BAGTEBIOLOOY. 



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 ofE in water), 

 and the aniline-water gentian-violet solution dropped 

 upon them; this is allowed to remain three or four 

 minutes, is poured off, aud 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, (^^^elch.) A very clear, sharply cut 

 picture usually follows this method of procedure. 



Staining of Spoees. — 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 



