NEUROLOGICAL METHODS. 399 



Tht 1 material is to be hardened in bichromate and imbedded 

 in celloidin in the usual way. The hardened blocks of cel- 

 loidin are brought into a mixture of equal parts of a cold 

 saturated solution of neutral acetate of copper and 10 per cent, 

 aqueous solution of potassio-tartrate of sodium (C 4 H 4 6 KNa 

 + 4HoO, salt of Seignette). They are left in the mixture for 

 twenty-four hours in an incubator. (Large specimens [pons] 

 will require forty-eight hours, the mixture being changed for 

 fresh at the end of twenty -four hours.) They are then 

 brought for twenty-four hours into aqueous solution of 

 neutral acetate of copper, either saturated or diluted with 1 

 volume of water, being kept as before in the incubator. 

 They are then rinsed with water and brought into 80 per 

 cent, alcohol, in which they may either remain till wanted or 

 be cut after half an hour. 



Sections are made and stained for from four to twenty-four 

 hours at the temperature of the room in a freshly prepared 

 mixture of 9 vols. of (A) a mixture of 7 c.c. of saturated 

 aqueous solution of carbonate of lithium with 93 c.c. of water, 

 and 1 vol. of (B) a solution of 1 grm. of haematoxylin in. 10 

 c.c. of alcohol (A and B may be kept in stock, but A must not 

 be too old). The sections should be loose ones, not such as 

 have been seriated in celloidin, and should not be thicker 

 than 0*025 mm. The stain is poured off and the sections 

 are washed in several changes of water poured on to them. 

 They are then treated with 90 per cent, alcohol, followed by 

 carbolic -acid-and-xylol mixture (for a short time only), or by 

 a mixture of 2 parts of anilin oil with 1 of xylol, then pure 

 xylol and xylol balsam (not chloroform balsam, which injures 

 the stain). 



Medullated fibres dark blue on a light, sometimes rosjr 

 ground. If it be wished to have the ground particularly 

 colourless, take instead of the second wash-water a mixture 

 of to J volume of common (not glacial) acetic acid with 100 

 volumes of water. Thick sections or series in celloidin re- 

 quire a special differentiation. They may be differentiated 

 either with the above-mentioned acetic acid mixture, or in 

 the usual borax-ferricyanide mixture diluted with water. In 

 the latter case the ground will be yellow. 



If the impregnation with the copper be imperfect (as, for 

 instance, may happen if the treatment with the copper salt 



