METHYLEN BLUE. 237 



In neither case should either ammonium picrate or methylen 

 blue be added to the medium. 



Preparations that have been fully differentiated by ammonia do not keep 

 more than a fe\v weeks; whilst those in which the differentiation has not 

 been carried to the point of thorough tinctorial isolation of the "neuro- 

 tibrils" have kept for five or six years (APATHY, Mitth. ZooL Stat. Neapel, 

 xii, 1S97, p. 712). 



Preparations preserved by these methods (I do not know 

 whether it is the case with preparations preserved by PARKER'S 

 or BETHE'S method, next section) are extremely sensitive to- 

 the influence of light. APATHY finds that lamplight is par- 

 ticularly injurious, especially the intense lamplight used 

 with high powers. 



329. Methods for Sections. None of the preceding methods 

 can be said to be anything like perfectly satisfactory. They 

 do not give preparations that will resist the operations 

 necessary for imbedding in paraffin. The stain is generally 

 not preserved in its true blue colour, but turns to a grey, 

 varying in tone from reddish browi* to bluish or greenish 

 black. The preparations seldom keep even in that state for 

 more than a very few months, and it is not satisfactory to be 

 obliged to mount preparations only in aqueous media. A 

 strong solution of platinum chloride is said to give a fixation 

 that will resist the treatment necessary for imbedding either 

 in celloidin or paraffin (see FEIST, Arch. f. Anat. und Entw., 

 1890, p. 116 ; Zeit. f. wixs. Mik., vii, 2, 1890, p. 231) ; but 

 the precipitate it gives is a flocculent one, and the prepara- 

 tions are not very satisfactory. 



.For the earlier method of PARKER (Zool. Anzeig., No. 403, 

 1892, p. 375) with methylal see previous editions. Later 

 (Mitth. ZooL Stat. Neapel, xii, 1895, p. 4) he fixes the stain 

 by dehydrating the objects in successive alcohols of 30, 50, 

 70, 95, and 100 per cent, strength, each containing 8 per 

 cent, of corrosive sublimate, then brings them into a mixture 

 of the last with an equal volume of xylol, and lastly into 

 pure xylol. 



The method of BETHE (Arch. f. mik. Anat., xliv, 1894, 

 p. 585), in its first form, is as follows : A solution is made 

 of 



