71 



198. Neurofibrillae (Simarro-Cajal Methods). Three of Ca- 

 jal's methods may be given : Formula 3a. 1 . Fixation in ammonia- 

 cal alcohol (2 to 10, usually 4 to 5, drops of ammonia per 50 c. c. of 

 95% alcohol), 20 to 48 hours; 2. Mop up with absorbent paper and 

 3. Place in !>% silver nitrate solution for 4 to 5 days at 32 to 40 C. ; 

 the tissue when ripe should be light gray; 4. Wash for a few minutes 

 in distilled water; 5. Reduce in a solution of 1 to 2 grams hydro- 

 chinon or py rogallol ; water, 100 c. c.; formalin, 5 c. c.; for 24 hours; 

 6. Wash in w T ater; 7. Imbed by the paraffin method; 8. Section 

 and mount in balsam or damar. Recommended for spinal cord, 

 cerebellum, spinal ganglia. 



Formula l^a. 1. Fix small pieces of tissue (5 mm. thick or less) 

 for 6 to 12 hours in formalin, 15 c. c., water 85 c.c.; 2. Wash 6 

 hours or longer in running water; 3. Place for 24 hours in 50 c. c. 

 of alcohol with 5 drops of ammonia added; 4. Mop with absorbent 

 paper; 5. Place in 1^% silver nitrate solution for 4 to 5 days (35 

 to 38 C.); The remaining steps as in formula 3a. Recommended 

 for sympathetic ganglia, cerebrum, cerebellum. 



Formula 5a. 1. Fix small pieces for 6 to 8 hours in water and 

 pyridin, each equal parts; then for 18 to 24 hours in pure 

 pyridin; 2. Wash for several hours in running water; 3. Place 

 in 90% alcohol for 1 day ; 4. Mop with absorbent paper; 5. Place 

 in \Yi% silver nitrate solution for 4 to 5 days (35 to 38 C.); The 

 remaining steps as in 3a and 4a. Recommended for embryonic and 

 fetal tissue (neurogenesis), regeneration, cerebrum. 



By these "photographic" methods, fibrillae, fibrillar networks, 

 changes in histogenesis, etc., may be demonstrated. 



For other methods of demonstrating the neurofibrillae, Biel- 

 schowsky's, Bethe's toluidin blue method, Apathy's hematein 

 method, etc., consult larger wwks on technique [6, 30], 



199. The Weigert Method for staining differentially the 

 myelin of myelinic nerve fibers. This method in all its various 

 forms, depends upon the power of the myelin, probably through the 

 reducing fatty acid present, to combine w r ith and hold in (nearly) 

 insoluble form the chromium (oxid), which thus serves as a pri- 

 mary mordant for a copper or iron hematoxylin stain, which is sub- 

 sequently differentiated by an oxidizer as a bleacher. The important 

 steps are: (1) fixing and mordanting in dichromate solutions; usually 

 the potassium salt is chosen; (2) a second mordantage in copper 

 (acetate), (3) the staining; (4) the differentiation. The point at 

 which the imbedding and sectioning are introduced is of secondary 



