416 NERVOUS SYSTEMSPECIAL METHODS. 



p. 673, and for pathological specimens ALZHEIMER'S methods 5, 6 and 9 

 in Histol. u. Histopath. Arb. uber d. GrossMrnr, iii, 1910, pp. 406 412, 

 which may be useful for the study of nerve-cells though originally pro- 

 posed for the investigation of neuroglia. 



B. Methods for Cells and Fibres, demonstrating Neurofibrils. 



833. Neurofibrils ; General Characters. Nerve cells and the fibres 

 into which they are prolonged contain, in addition to the chromatic 

 constituents shown by the methods already dealt with, a character- 

 istic so-called achromatic element, consisting chiefly of very fine and 

 fairly refractive fibrils which can only be seen with great difficulty 

 in the unstained state, but may be fixed with osmic acid and made 

 out in thin sections of medullated nerve fibres observed in diluted 

 glycerin or water, and may be to a certain extent isolated by macera- 

 tion. For their demonstration, however, one or the other of the 

 methods chronologically described in the following paragraphs must 

 be employed. They are all regarded as giving true stains of neuro- 

 fibrils. 



For the method of KUPFER (Sitzb. math. Kl. Akad. Wiss. Munchen, xiii, 

 1884) see former edition. 



834. APATHY'S Methods. The gold method (" Nachvergoldung ") 

 has been given in 371. The stain is very sharp, but good results 

 are obtained only in certain invertebrates, and even in these with 

 considerable difficulty. 



The hcemateine method (Mitth. Zool. Stat. Neapel, xii, 1897, p. 712) 

 has the same advantages and disadvantages, and has been little used 

 since the discovery of the Cajal and Bielschowsky processes. Material 

 may be fixed with corrosive sublimate, Zenker's fluid, picro-sulphuric 

 acid, or any other mixture which is not inimical to staining with 

 alum hsematoxylin, and should be preserved in 90 per cent, alcohol. 

 Portions, no more than J cm. thick, are stained for at least forty- 

 eight hours in hsemateine I. A. ( 259), and then washed for up to 

 twenty-four hours in absolutely pure distilled water, or preferably 

 suspended therein. Before the stain has become washed out of the 

 neurofibrils entirely, it is fixed by putting the preparations for 

 three to five hours into spring water, after which they are put back 

 for not more than two hours into distilled water, dehydrated as 

 rapidly as possible by hanging them up in absolute alcohol, and 

 embedded in paraffin or celloidin, after clearing with chloroform, 

 and carefully protecting them from light whilst in chloroform or 

 celloidin. The sections are mounted either in a resin or in neutral 

 glycerin. 



