460 NERVOUS SYSTEM—GENERAL METHODS 



Ammonium bichromate should at first be employed at half 

 the strength reeomniended for potassium bichromate ; it can 

 subsequently be raised to as much as 5 per cent, for the cere- 

 bellum towards the end of the hardening. 



See also Bonvicini {Ztschr. wiss. Mikr., xxvi, 1909, p. 412). 



Rawitz {ibid., p. 338) puts formol material for exactly five 

 days into alcohol with 10 per cent, tinctura iodi P. G., then for 

 eight to ten days into saturated solutions of potassium bichromate 

 changed after the first day, and lastly into 95 per cent, alcohol 

 for three days in the dark. 



The methods of Nissl (Enzykl. Mik. Techn., ii, 1910, p. 245), Betz 

 (Arch. mikr. Anat., ix, 1873, p. 101), Lewis {Human Brain), Hamilton 

 {Joiirn. Anat. and Physiol., xii, 1878, p. 254), Duval {Journ. de VAnat., 

 xii, 1876, p. 497), Deecke {Jonrn. R. Micr. Soc, 1883, p. 449), are no 

 longer used. 



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985. Other Reagents. Small pieces can be fixed in Zenker^s 

 fluids or in Zenker-formalin (Helly, Maximow) as described in 

 § 78. The pieces are best imbedded in paraffin. The sections 

 can be stained by Mallory's eosin-methylen blue method (§ 342), 

 Mann's methyl blue and eosin method (§ 356), Mallory's phos- 

 photungstic acid-ha;matoxylin method for neuroglia and other 

 methods. 



Bouin's fluid (§ 115) can also be usefully employed for rela- 

 tively small pieces, which can be imbedded either in celloidin 

 or paraffin, the picric acid being extracted during dehydration 

 by means of potassium or lithium iodide added to the weaker 

 alcohols. Or after removal of the picric acid they are stained 

 in bulk with haematoxylin and eosin as advised by Da Fano 

 {vide § 999 and Journ. Physiol., Ix, 1925, p. 1) chiefly for spinal 

 and sympathetic ganglia and the central nervous system of 

 small animals. Especially beautiful differential staining with 

 van Gieson's mixture can be obtained either after primary fixation 

 or after-hardening in Bouin's fluid. Paraffin sections of the 

 nervous system, fixed in this way, may be stained for neuroglia 

 by Victoria Blue (Anderson's modification, g'.t'.). It is unnecessary 

 to remove the picric acid from the block completely before cutting 

 it. It may be removed from the section by treatment with warm 

 distilled water or by a prolonged wash in alcohol. 



Osmic acid can be employed alone only for very small pieces, 

 but it is useful for special purposes ; its penetrating power can 

 be enhanced by keeping the vessels at temperatures varying 

 between 20° and 40° C. (see further on this subject, § 40). 



Chromic acid is rarely used alone. Its action is rapid, but uneven, 

 and causes shrinkage and brittleness. A very little {e.g. 3 to 5 drops of 

 a 1 per cent, solution to every 100 c.c. of fluid), added to bichromate 

 solutions will do no harm and quicken the hardening. 



