SPECIAL METHODS. 247* 



plants in boiling water as quickly as possible and hardened 

 them, before cutting, in absolute alcohol. 



Concerning the strength of the sulphuric acid used for 

 swelling it may be remarked that it has been used partly in 

 concentrated form, partly after dilution with one fourth its- 

 volume of water. With membranes which swell strongly,, 

 the dilute acid is, of course, to be preferred. The time for 

 it to act depends chiefly on the character of the membranes.. 

 But usually a few seconds is sufficient for concentrated acid- 

 The acid must, of course, be removed by careful washing irv 

 water, before staining. 



453. The following dyes have been used for staining sec- 

 tions treated in this way. 



1. Hofmanris blue (same as aniline blue). Gardiner (II) 

 recommends a solution of this dye in 50$ alcohol saturated 

 with picric acid. The solution is washed out with water,, 

 and the preparation is then either mounted in glycerine, or 

 is gradually transferred through dilute to strong alcohol,, 

 cleared with clove-oil, and mounted in Canada balsam. In 

 this way very permanent preparations of the protoplasmic 

 connections may be obtained. 



Gardiner also used a solution of Hofmann's blue in 50^ 

 alcohol acidified with a few drops of acetic acid. The sub- 

 sequent treatment is the same as in the previous case. 



Terletzki (I, 455) stains simply with a strong aqueous- 

 solution of aniline blue and examines the preparation in 

 water, after washing. 



2. Hofmanris violet is used by Gardiner, simply in an 

 aqueous solution. This at first stains wall and protoplasm 

 about equally ; but, after lying for a long time in glycerine, 

 in many cases several days, the color is removed from the 

 walls, while the protoplasts and protoplasmic connections 

 remain strongly stained. 



3. Methyl violet is recommended by Kienitz-Gerloff (I, 9) 

 for such cells, like those of hairs, etc., as do not permit the 

 penetration of Hofmann's blue, on account of cuticulariza- 

 tion of the walls. He uses it in a concentrated aqueous 

 solution. 



