272 XXI. BACTERIA YEAST. 



if oil of cloves is used for clearing, for this extracts the colouring 

 matter, more or less completely, according to the time during which 

 action is permitted. For the same purpose it has also been recom- 

 mended to immerse the preparation (after rinsing in water) for 

 one second in 0-5 per cent, acetic acid. Overstained preparations, 

 from which a portion of the colour has been removed, often give 

 the most beautiful figures. If it is to be kept, the clearing fluid 

 should be removed by blotting-paper, and the preparation mounted 

 preferably in Canada balsam. The Canada balsam should, how- 

 ever, be dissolved in xylol or in turpentine, not in chloroform, since 

 this latter extracts these basic aniline colours ; and for the same 

 reason the Canada balsam must not be used warm. For per- 

 manent preparations a little overstating is no disadvantage, since 

 in Canada balsam the depth of the colour in time diminishes. If 

 the preparation should ever be used with a homogeneous immer- 

 sion lens, we must take care that the Canada balsam does not 

 extend from under the edge of the cover-glass, since it is soluble 

 in the immersion oil, and the entire cover-glass may thus be fouled. 

 To prevent this the edge of the cover-glass can, after the Canada 

 balsam is set, be covered with a narrow band of gold-size, which 

 is insoluble in the immersion oil. This is done with a fine camel- 

 hair brush, care being taken that the gold- size does not extend 

 further than necessary over the cover-glass. Preparations stained 

 in Bismarck brown or Vesuvin retain their colour also in glycerine, 

 and can therefore be preserved in it. The closing of the edge of 

 the cover-glass is then effected by means of Canada balsam dis- 

 solved in chloroform, and after some days or weeks, as convenient, 

 the balsam can be covered with the band of gold- size as above. 

 These latter stained preparations can also be embedded in glycerine- 

 jelly, and then need no further closing. 



If material in spore-formation has appeared in our culture, 

 we may perhaps have noted in our attempts at staining that the 

 spores remain unstained. This arises from our manipulations thus 

 far not having led to the death of the spores, so that they do not 

 absorb the stain. But if we pass the air-dry cover-glass prepara- 

 tion sufficiently often through the flame, say eight to ten times, 

 the spores afterwards stain ; but at the same time the other 

 parts of the spore-forming bacteria, as well as those not fructifying, 

 and also the cytoplasm and nuclei of any tissue elements in the 

 preparation, lose more or less completely their capacity for stain- 

 ing. The same effect is produced if we allow the air-dry cover- 



