422 NERVOUS SYSTEM SPECIAL METHODS. 



I understand from Cajal's pupil, Del Rio Hortega, that this 

 formula may be successfully employed for the study of peripheral 

 nerve endings. In this case material is better fixed for twenty-four 

 hours in pyridine to which one-third its volume of distilled water 

 or 96 per cent, alcohol has been added. Pieces should be washed 

 in running tap-water overnight and then transferred for six hours 

 into pure 96 per cent, alcohol. Impregnation, reduction, embedding, 

 etc., as .above. Eesults are good, but pieces become extremely 

 hard even if dehydrated very quickly, and are consequently 

 difficult to cut. See also Formula 5a. 



Formula 2a, C. Fix for twenty-four hours in 50 c.c. of alcohol 

 with 10 drops of nicotine. Mop up with blotting paper, without 

 washing, and silver as usual for five days (or four at 40 C.). Good 

 results with adult tissues, especially spinal cord. Good penetration 

 and less shrinkage than with pure alcohol. 



Formula 2a, D. Fix for twenty-four hours in allyl alcohol (the 

 industrial product will do). Wash for some hours in several changes 

 of water. Put for a day into 50 c.c. of alcohol with 4 drops of 

 ammonia. Silver for four days at 35 to 38 C., and reduce as usual. 

 Good for human tissues, especially for fibre plexuses of cerebrum 

 and cerebellum. Instead of allyl alcohol one may take acetal or 

 acetone. Put for six hours into acetone with 25 per cent, of water, 

 then for twenty-four into pure acetone, wash in water, etc., as above. 



Formula 3a. Fixation in ammoniacal alcohol for twenty to forty- 

 eight hours. The most generally useful formula is 50 c.c. of 96 per 

 cent, alcohol with 4 to 5 drops of ammonia (of 22 strength). But 

 for cerebrum not more than 1 to 3 drops ; for cerebellum, ganglia, 

 spinal cord and regenerating tracts, 4 drops ; for neurofibrils of the 

 large nerve cells of the medulla oblongata and spinal cord, 9 to 10 

 drops. To avoid shrinkage, it is well to begin by putting the pieces for 

 six hours into 70 per cent, alcohol, then in 85 per cent., without 

 ammonia ; then for the rest of the time into the ammoniacal alcohol. 

 Do not wash, but mop up with blotting paper before putting into 

 the silver. Silver for four to four and a half days (small specimens) 

 at 40 C., or medium to large (3 to 4 mm. thick) for five days at 

 32 to 35 C. So long as the tissues are only yellowish- white, they 

 are 'not ripe for reduction ; light grey indicates ripeness ; dark grey 

 over-ripeness. Reduce as by Formula la. 



Specimens may be decalcified, after reducing and washing, 

 in 96 per cent, alcohol to which a few drops of nitric acid have 

 been added. 



For the delicate impregnation of the neurofibrils of the large and 



