208 CHAPTER XVI. 



prepared gam-arabio solution. When thorouglily penetrated 

 with this they are removed and mounted in the following 

 gam-syrup medium [loc. ait., p. 37) : 



Picked gum-arabic . . .50 grms. 



Cane-sugar (not candied) . . 50 „ 



Distilled water . . . . 50 „ 



Dissolve over a water-bath and add 0"05 grm. thymol. 

 (This mounting medium sets quickly and as hard as balsam, 

 so that no cementing of the mounts is necessary. Farrants' 

 medium [with omission of the arsenious acid] will also do. 

 In neither case should either ammonium picrate or methylen 

 blue be added to the medium.) Preparations that have 

 been fully differentiated (§ 342) do not keep more than 

 a few weeks ; whilst those in which the differentiation has 

 not been carried to the point of thorough tinctorial isolation 

 of the neuro-fibrils have kept for five or six years (Apathy, 

 Mitth. Zool. Stat. Neapel, xii, 1897, p. 712). 



Pleschko {Anat. Ana., xiii, 1897, p. 16) fixes with picrate, 

 and then puts into 10 per cent, foi'mol for a few days. 



The methods described next § are also available for 

 material not destined to be sectioned. 



344. Methods for Sections. — The preceding methods do not 

 give preparations that will resist the operations necessary 

 for imbedding in paraffin or mounting in balsam. A strong- 

 solution of platinum chloride is said to do this (see Feist, 

 Arch. Anat. Entw., 1890, p. 116), but the preparations are 

 not very satisfactory. 



For the earlier method of Packer [Zool. Anxeig., 1892, p. 

 375) with methylal see eai-ly editions. Later {Mitth. Zool. 

 Stat. Neapel, xii, 1895, p. 4) he fixes the stain by dehy- 

 drating 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. 



For the earlier method of Bethe {Arch. mile. Anat., xliv, 

 1894, p. 585), see last edition. 



Bethe's later method {Anat. Am:., xii, 1896, p. 438) is as 

 follows : After staining, pieces of tissue of 2 to 3 mm. 



