NERVOUS SYSTEM — OYTOLOGIOAL METHODS. 391 



old. But tlii8 must be about tlie limit, for I find material 

 seven years old entirely refractory. 



The two methods do not give quite the same images of 

 neurofibrils. Eamon's tends to show intra-cellular fibrils 

 anastomosiDg into netwoi'ks, whilst Bielschowsky's (like 

 Bethe's) tends rather to show independent fibrils traversing 

 cells without anastomosing. 



For the demonstration of pericellular networks, bnds of 

 Held and Auerbach, non-medullated fibres and nerve- endings 

 in general Ramon's seems the better. 



Bielschowsky's method stains elastic fibres and connective 

 tissvie fibi'es, which Ram6n's do not. 



768. Ramon t Cajal's Methods. — This section contains all 

 the methods described by Ramon in Trabajos del Lab. de 

 Investigaciones Biologicas, viii, 1910 (t. xiii of Rev. trimes- 

 tral micrografica) . The numbering is that of Ramon. 



Formula la. — For small and medium nerve-cells. Small 

 pieces of fresh tissue are put direct {i. e. without previous 

 treatment with any other reagent) into nitrate of silver of 

 I'o per cent. 



They are kept for about three days (2| for very small 

 objects, such as spinal cord of newborn rabbit ; 4 for 

 medium-sized, such as cord or cerebellum of adult rabbit ; 

 5 for specimens of the size of its cerebrum) in the silver. 

 They must be kept in a stove at a temperature of about 

 .35° C. all the time. (In summer, with a temperature con- 

 stantly over 22° C, the stove may be dispensed with, provided 

 that the impregnation be prolonged for two or three days 

 more.) The tissues are known to be ripe for reduction when 

 a freshly cut surface shows a brownish-yellow coloration. 



They are then washed for one or two minutes in distilled 

 water, and put into — 



Pyrogallol or hydroquinon . 1 to 2 grm. 



Water ... 100 „ 



Formol* . . . 5 „ 



* The formol is not necessary, but is useful. You may take pyridin 

 instead (1 to 3 per cent.). Ton may also add 0'5 per cent, of sodium 

 sulphite. The stronger the pyrogallol the greater the contrast: it is 

 sometimes useful to take as much as 3 per cent., hut then the over- 

 impregnation of the outer layers will be increased. Hydroquinon (I add) 

 reduces more energetically than pyrogallol. 



