364 NERVES. 



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

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



The process is applicable to tissues that have been 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 solu- 

 tion. 



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

 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 hsematoxylin, 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 superseded by the copper process.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 the former, due to 

 MAX FLESCH, has some advantages, and is given in the next section. 



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 

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

 2'5 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 the 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 

 instead of pure hsematoxylin. One part of commercial extract of logwood is 

 dissolved in 90 parts of water and 10 of alcohol. To the filtered solution is 

 added 8 drops of concentrated solution of lithium carbonate for each 100 c.c. 

 Sections require from eighteen to twenty-four hours in the stain at the 

 normal temperature. 



BREGLIA (ibid., vii, 2, 1890, p. 236 ; see also Journ. Roy. Mic. Soc., 1890, 

 p. 817) stains with liquid extract of logwood or Pernambuco wood, prepared 

 by extracting 7 to 10 grms. of the wood for 5 or 6 days with 100 c.c. of alco- 

 hol of 90 to 95 per cent. 



The results obtained by Weigert's method are most splendid. 

 The blue-black nerves stand out with admirable boldness on 

 a golden ground. The method is applicable to the study of 

 peripheral nerves as well as to nerve-centres, and is likely to 

 be of great utility in Vertebrate embryology. 



Nerve-tissue is not the only tissue stained by the process, 

 which can be usefully applied to lymphatic glands and to 

 skin (see SCHIEFFERDECKEB, in Anat. Anz., ii, 1887, p. 680). 



