CHAPTER XXXII. 423 



medium nerve cells this formula is superior to all others. It gives 

 good results with the majority of nerve centres, and is particularly 

 good for non-medullated fibres, peri-cellular baskets of cerebellum, 

 buds of Held and Auerbach in the oblongata, for human sympathetic, 

 and for the study of regenerating nerve fibres. 



Formula 3a, A. Fix in 50 c.c. of alcohol with 10 grms. of glycerin 

 and 6 to 10 drops of ammonia. Good for retina and non-medullated 

 fibres, but especially for the buds of Held and Auerbach. 



Formula 3a, B. Fix in 50 c.c. of alcohol with 1 -5 c.c. of a 33 per 

 cent, alcoholic solution of ethylamine. Results the same as with 

 ammoniacal alcohol. 



Formula 4a. Pieces of tissue of not more than 4 mm. in thickness 

 are fixed for six to twelve hours in 15 per cent, formol. Wash for 

 six or more hours in running tap-water. Put for twenty-four hours 

 into 50 c.c. of alcohol with 5 drops of ammonia. Wipe with blotting 

 paper, silver for five days (or four if the stove is at 38 to 40 C.). 

 The rest as usual. Sharp impregnation of the finer fibres of nerve 

 centres and of the terminal buds of pericellular nests. Adult tissues 

 give better results than young ones. Energetic stain of the arborisa- 

 tions of the moss fibres of the cerebellum. 



Formula 4a, A. Fix in " a mixture of formol and alcohol." 

 Wash out thoroughly with running tap-water, silver, and reduce 

 as usual. Fixation more rapid and better ; results similar to those 

 of 3a. 



Formula 5a. This is characterised by a preliminary fixation in 

 pyridine as originally suggested by HELD (Arch. Anat. PhysioL, 

 Anat. Abth., 1905, p. 77 ; Anat. Anz., xxix., 1906, p. 186). He 

 used to fix tissues in pure pyridine, but Cajal finds that this is 

 likely to cause much shrinkage, and he recommends fixing small 

 pieces first for six to eight hours in a mixture of equal parts of 

 distilled water and pyridine, then for eighteen to twenty-four 

 hours into pure pyridine. Wash for several hours in running 

 water, and put for a day into 90 per cent, alcohol. Wipe, and 

 put for four to five days into 1 -5 per cent, silver nitrate at 35 to 

 38 C., and reduce as usual. Not very good for adult organs, but 

 superior to all others for the earliest phases of neurogenesis, and 

 good for regenerative processes, as well as for peripheral nerve 

 endings. 



Formula 6a. Put for twenty-four hours into 50 c.c. of water 

 with 5 grms. of chloral hydrate, rinse, and put into 50 c.c. of 96 per 

 cent, alcohol with 5 drops of ammonia (time not stated). Wipe 

 with blotting paper ; put for four to five days at 35 to 38 C. into 



