METHODS. 11 



be removed, and washed for a short time in alcohol ; then they 

 must be placed in absolute alcohol and kept there until they 

 appear transparent. The sections can now be mounted in dis- 

 tilled water in order to see if the results are satisfactory, or, if 

 they are to be preserved, they must be cleared by means of oil of 

 cloves, and mounted in Canada balsam or Dammar. 



By this means very successful preparations of the structure of 

 nuclei can be obtained. 



2. Fuchsin. This is used in alcoholic solution. It is useful 

 for bringing out the structure of thickened cell- walls. The sections 

 must be previously treated with alcohol. It is also a good reagent 

 for corky tissue. When a section is stained and is then washed 

 with absolute alcohol, the coloration is removed from all parts 

 excepting the corky tissue. 



3. Methyl-green. A tolerably strong alcoholic solution of 

 this is used. The sections of the object, which must have been 

 previously kept in absolute alcohol, are to be treated with the 

 staining-fluid for from 5 25 minutes, then quickly washed with 

 distilled water, and mounted in glycerine. The nucleus stains 

 of a green or bluish-green colour, the protoplasm remaining un- 

 coloured. It is especially good for staining nuclei which are 

 dividing. It has been used for staining chlorophyll-corpuscles, 

 and is also useful in bringing out the nuclei and protoplasm in 

 the cells of Fungi, which have been previously preserved in 

 absolute alcohol and in glycerine. 



Strasburger recommends the following method for obtaining 

 preparations of nuclei : A section of the fresh tissue is mounted 

 in 1 per cent, acetic acid solution, to which a little methyl-green 

 has been added ; the nuclei are fixed almost instantaneously. 



4. Methyl- violet, This is used in concentrated alcoholic 

 solution. It is especially useful for staining bacteria. A few drops 

 of the solution are added to 15 20 c.c. of distilled water, and a 

 drop or two of the mixture should then be placed on the bacteria- 

 membrane (zooglcea), and be allowed to remain there for a short 

 time until the membrane appears to be coloured : if the solution 

 used is too strong, the substance between the bacteria will become 

 stained. The colouring-matter is then washed off with distilled 

 water, or better with a 10 per cent, solution of acetate of potash. 

 The preparation may then either be allowed to dry in the air and 



