404 



PRESERVING AND STAINING 



The osmotic pressure for concentrations between those given in this 

 table are proportional to the values between which the particular con- 

 centration lies. 



VI. Preserving and Staining. — To preserve material for ana- 

 tomical investigation, ordinary methylated spirit will usually 

 serve, provided there is at least four times the volume of liquid 

 as of material. For showing nuclear structure, however, other 

 fixatives are employed (cf. Chamberlain, Metliods in Plant His- 

 tology), e.g. acetic alcohol, made by adding one part of glacial 

 acetic acid to four parts of alcohol. After remaining in this for 

 a few minutes up to several hours, according to the texture of 

 the material, the latter is transferred to ordinary spirit. 



For staining, the thinnest sections (cf. VIII below) should be 

 placed in a few drops of safranin,' on a slide, for from five to 

 fifteen minutes, more safranin being added at intervals to replace 

 that lost by evaporation. The excess of the stain is now removed 

 by washing the sections with spirit, and then a few drops of 

 Kleinenberg's hcematoxylin are allowed to act for half a minute. 

 After this the sections are washed with spirit, and permanent 

 preparations are made in the following way : 



The spirit is changed several times, and finalh' replaced by 

 a few drops of absolute alcohol. In this way dehvdration 

 {i.e. removal of water) is effected. To the alcohol a drop or two 

 of clove oil is then added, and this mixture is in turn replaced 

 by pure clove oil. The sections should now become transparent, 

 and, if this fails to occur, they have not been sufhciently de- 

 hydrated. After two to three minutes the oil is poured off, 

 and Canada balsam, dissolved in xylol, added. A cover-glass 

 is then carefully let down on to the sections, and the slide placed 



' Or methyl blue can be used, the sections being left in this for about 

 half a minute. 



