396 CHAPTKR xxxn. 



Formula 7a. Fix for 24 hours in Merck's fibro-lysin, 

 wash for 6, put for 24 into 50 c.c. of alcohol with five drops 

 of ammonia. The rest as usual. 



Instead of fibrolysin, lysidin may be taken. 



Application of the Foregoing Method* to Different Objects- of 



Study. 



(1) For the study of the evolution of neuroblasts and nerve 

 fibres in very early embryos, it is absolutely necessary to avoid 

 fixing with formol, or alcohol with an accelerator, or am- 

 moniacal liquids. The best formulas are 2a and 5a. Applic- 

 able to all vertebrates, but preferably to embryos of birds 

 and fishes. 



(2) For late embryos and fwti of mammals. Besides the 

 above, 3a, 6a and alcohol with an accelerator. Best subjects, 

 embryos of chick from the fifth day, and of rabbit from the 

 tenth to the twelfth. Or newborn birds, with ammonia 

 alcohol or 5a. 



(3) For sympathetic ganglia. Formula 3a, or pure alcohols 

 or 4a and 5a. Best with man. Dog, cat, and rabbit give 

 mostly weak reactions. The visceral ganglia are the most 

 difficult. 



(4) Sensory ganglia. Formula 2a, or 3a. Easy. 



(5) Cerebellum. The most favourable of all nerve centres. 

 For Purkinje cells, la or 3a. For the baskets, climbing 

 fibres, and medium and small dendrites, 2a, or its variants. 

 For terminal rosettes and collaterals of mossy fibres, and for 

 the plexuses of the granular layer, 4a, or sometimes 5a or 6a. 

 For the stellate cells of the molecular layer, 2a arid 3a, on 

 the dog. 



(6) Cerebrum. In general, the same formulae as for the 

 cerebellum, especially la, for pyramids of young dogs and 

 cats (of eight to twenty days). In formula 3a, the propor- 

 tion of ammonia should be .diminished. For fine plexuses, 

 4a, 5a, and 6a. 



(7) Spinal cord and buJb. All the formulas are applicable. 

 Fur neurofibrils of motor cells the best subject is the dug 

 of four to fifteen days, with formula 3a, with a large dose of 

 ammonia (ton drops). Also the alcoholic fixatives with an 

 accelerator. For medntlated fibres, large and small, 2;i. or 



