34 Neurological Technique 



1 1. In either case transfer them from water to the i per cent, 

 formic acid solution (D) for about 2 minutes. 



12. Rinse by dipping each slide several times through fresh 

 distilled water and then, 



13. To impregnate, immerse the slides in a vessel of the i per 

 cent, gold chloride solution (C) for 24 hours. 



Avoid direct sunlight during this period. 



14. To reduce, rinse off surplus gold chloride by simply dipping 

 each slide into distilled water and transfer to a copious amount 

 of the I per cent, formic acid solution (D), and expose to 

 continuous sunlight till sufficient reduction of the gold has taken 

 place. This usually occurs in from 4 to 8 hours. The sections 

 assume a rich purple color. 



The following precautions are urged as essential to the attain- 

 ment of the best results : (i) The period of sunlight should be 

 unbroken. (2) The light should be as bright, and at the same time 

 the temperature as low, as possible, or not above 20° C. In 

 winter the vessels may be placed in direct sunlight on a window 

 sill in a cool part of the room. In summer direct sunlight must 

 be avoided or artificial means of maintaining a low temperature 

 be employed. (3) The illumination must be as uniform as possible. 

 To insure this it is advised that sheets of white paper be placed 

 under the vessels and, as reflectors, also on the side opposite the 

 light. (4) In order to prevent the collection of falling precipi- 

 tates on the sections, the slides must be placed in a sloping posi- 

 tion with the sections on the under side. Stoppered tubes are 

 suggested for this purpose, one for each slide. These may be 

 inclined at any angle. (5) If the formic acid solution becomes 

 colored, it should be renewed. (6) During the reduction, the 

 preparations should be jarred or moved about as little as 

 possible. 



15. To mount. After reduction, rinse a few minutes in dis- 

 tilled water and mount directly in glycerine or glycerine jelly 

 (E). Warm the jelly before using. 



Or, equally well, the sections may be dehydrated by passing 

 them successively through the increasing grades of alcohol (50 



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