84 METHYLEN BLUE, AND OTHER ANILINS. 



paragraph on "Preservation of the Preparations" ( 119). 

 This is done by pouring the liquid over them, and leaving 

 them in it without moving them about in it for at least an 

 hour, and by preference in the dark. The further treatment 

 is as described in 119. 



The object of the ammonia in these liquids is to differentiate 

 the stain to produce an artificial " secondary differentiation." 

 It acts by washing out the absorbed colour from certain 

 elements, others resisting its action longer, much as HC1 

 alcohol washes out a borax-carmine stain. In this case the 

 elements that are washed out are the protoplasmic parts of 

 nerve-fibres, and their " interfibrillar " and " perifibrillar " 

 substance, the " primitive fibrils " still retaining the colour 

 strongly. It is of theoretical interest to remark that accord- 

 ing to Apathy the coloration thus obtained is a true stain of 

 the " primitive fibrils," not an impregnation. The " primitive 

 fibrils" are sharply stained of a violet-blue, showing no 

 granular precipitate, and the " interfibrillar " and "perifi- 

 brillar " substance, as well as nuclei, are either colourless or 

 very lightly stained. The usual methods, on the other hand, 

 give an "inverse "reaction, the "primitive fibrils" remain- 

 ing colourless, whilst the interfibrillar substance and proto- 

 plasm of the nerve-fibres are impregnated with a finely 

 granular greenish-black or violet precipitate, and the nuclei 

 are usually stained. 



119. Preservation of the Preparations. There are consider- 

 able difficulties in the way of obtaining permanent preparations 

 of methylen-blue stains, as the stain is so very unstable that, 

 as above explained, it begins to discharge after a short time, 

 even in the living and not yet totally impregnated tissue. 

 The colour may, however, be fixed, and more or less permanent 

 preparations be made, by one or other of the following 

 methods : 



DOGIEL (Arch. /. mik. Anat., xxxiii, 4, 1889, pp. 440 et seq.), 

 following ARNSTEIN (Anat. Anzeig., 1887, p. 551), brings the 

 preparations, in order to fix the colour, into saturated aqueous 

 solution of picrate of ammonia, in which they are allowed to 

 remain for half an hour or more, and are then removed, 

 washed in fresh picrate of ammonia solution, and studied in 

 dilute glycerin, or mounted permanently in glycerin saturated 



