WEIGERT'S METHOD FOR MEDULLATED NERVES. 309 



two hours; medullary layers of brain, two hours; cortical- 

 layers, twenty-four hours. 



They are then rinsed with water, and brought into a de- 

 colourising solution composed of 



Borax 2-0 parts. 



Ferricyanide of potassium . . . 2'5 

 Water 200'0 



They remain in the solution until they are decoloured to 

 the right degree, that is, until complete differentiation of the 

 nerves (half an hour to several hours), and are then rinsed 

 with water, dehydrated with alcohol, and mounted in balsam. 

 They may be previously stained, if desired, with alum-carmine 

 for the demonstration of nuclei. 



For very difficult objects, such as pathological nerves, the decolouring 

 solution should be diluted with water, and the immersion in it prolonged. 

 GELPKE (Zeit. f. wiss. Mik., 1885, p. 489) states that for transverse sections 

 of atrophied nerves the solution should be diluted with fifty volumes of 

 water, and the immersion be prolonged to twelve hours at the least ; for 

 longitudinal sections it should be dilated with ten volumes of water. 



The process is applicable to tissues that have beeen hardened in alcohol 

 or in any other way, provided that they be put into a solution of a chromic 

 salt until they become brown, before mordanting them in the copper 

 solution. 



As above stated, it is not necessary that the mordantage be done in the 

 mass with tissues imbedded in celloidin. MAX FLESCH (Zeit.f. wiss. Mik., 

 iii, 1, 1886, p. 50) finds that this practice is unfavorable to subsequent 

 staining with other reagents than hseinatoxylin, and prefers (following 

 LICHTHEIM) to make the sections first, bring them on closet-paper into the 

 mordant, and after mordanting bring them on a spatula into 70 per cent, 

 alcohol, and thence into the stain. 



In the process given above, a copper lake is formed in the tissues. In the 

 earlier form of the process, the mordantage with the copper salt was omitted, 

 and the stain depended on the formation in the tissues of a chromic lake. 

 The results were not quite so good, and the process may be taken to be 

 superseded by the copper process. A modified form of, due to MAX FLESCH, 

 has some advantages, and is given in the next . 



If very many large sections have to be prepared, and if the staining solu- 

 tion be thrown away after using, the process may be found somewhat 

 expensive. The following method for regenerating the staining solution is 

 givi-n by FANNY BEELINEEBLAU (Zeit.f. wiss. Mik., 1886, p. 50) : About 

 jJ-"> to 5 per cent, of baryta water is added to the used solution ; it is well 

 shaken and allowed to stand for twenty-four hours ; carbonic acid (obtained 

 from llu> action of crude hydrochloric acid on marble) is led through it, it is 

 allowed to stand for twenty-four hours more, and then filtered. 



PANETH (ibid., 1887, p. 213) makes the stain with extract of logwood, 



