STAINING MEDULLATED NERVE-FIBRES. 231 



brittle. Wash the pieces for some hours in water after removing 

 from the hardening solution for examination. Cut sections either 

 by the celloidin or gum-freezing method. The latter is in most 

 cases quite sufficient for brain tissue. The sections may be pre- 

 served in alcohol in the ordinary way. 



The following is the proceeding that I have found most satis- 

 factory in carrying out Heller's process on these tissues : — Place 

 the sections in i per cent, osmic acid for half-an-hour (in the dark), 

 then in 5 per cent, pyrogallic acid for half-an-hour, ^ per cent, 

 potassium permanganate for three or four minutes (brain sections 

 for not more than one minute), i per cent, oxalic acid for three to 

 five minutes. Wash the sections in water after treatment with 

 each solution. Dehydrate, clear, and mount in balsam. 



I have now applied this modification of Heller's process 

 extensively to healthy and morbid nervous tissues, and I am satis- 

 fied that it presents great advantages as a method for demonstrat- 

 ing medullated fibres. The staining result is probably as distinct 

 as that furnished by the Weigert-Pal method, and it can be 

 obtained in a much shorter time. The whole process can be 

 carried out within a fortnight from the time the tissues are placed 

 in the hardening solution. The preparations are admirably 

 adapted for lantern demonstration and for photography, and they 

 are suitable for high- as well as low-power microscopic examina- 

 tion. They show degenerating fibres very distinctly, while tracts 

 in which the myelin has wholly disappeared are colourless. The 

 method gives excellent results with the delicate medullated fibres 

 of the brain, and on this account I believe, indeed, that it fur- 

 nishes what has for long been a great desideratum, especially for 

 the study of the morbid changes occurring in this tissue-element in 

 insanity. The sections may be satisfactorily counterstained in 

 various ways, haematoxylin especially giving good results. The 

 nerve-cells are beautifully preserved and stain fairly well. As yet, 

 however, I have not been able to obtain satisfactory staining of the 

 chromatic granules of the protoplasm. It seems probable that the 

 circumstance is due, as indicated above, to the strength of the 

 formalin in the hardening solution, and that, if this was reduced 

 to about 2 percent, these granules could be readily coloured by 

 the stains generally employed for the purpose. 



