346 PRACTICAL HISTOLOGY. [XXX. 



The sublimate may act on (a.) the ganglionic cells, (5.) the neuroglia cells, 

 and (c. ) the blood-vessels. The best results with these methods are obtained 

 with the cerebral cortex. The sections can be stained afterwards by the usual 

 methods, and particularly by Magdala-red. 



The parts acted on by the sublimate are white by reflected light, and appear 

 black by transmitted light, because they are opaque. Golgi 1 finds that for the 

 study of the diffuse network in the central nervous system, by this method the 

 best results are obtained when the " metallic white " is converted into a 

 metallic black. For this purpose he uses the "fixer" employed for. fixing 

 positive photographs on aristotypic paper. 



(A.) Water. . ' . . . I litre. 



Hyposulphite of soda . . . 175 grains. 



Alum . . . . 20 ,, 



Ammonium sulphocyanide . .10,, 



Chloride of sodium . . . 40 



Leave the mixture for 8 days and then filter. 



(B.) Water, . . . . 100 cc. 



Gold chloride. . . i gram. 



For the toning and fixing fluid, mix of 



A . . . . 60 cc. 



B 7 



Procedure. 



(1.) Wash in distilled water. 



(2.) Immerse sections (1-2 mins.) in the above mixture. The sections 



become black. 



(3.) Prolonged washing in water. 



(4.) (Optional.) Faint coloration of the sections with acid carmine. 

 (5.) Wash again, then mount in balsam. 



25. Double Impregnation Method of Eamon y Cayal. 2 Morsels of tissue 

 are placed in the dark in the osmico-bichromate mixture as for Golgi's rapid 

 method (2-3 days), and then they are gently washed and placed in .$-.75 

 per cent, silver nitrate (1-2 days). They are retransferred for 3-4 days to the 

 osmico-bichromate fluid (3-4-5 days), and then again to silver. They are then 

 hardened in alcohol and cut. This method certainly gives good results in 

 some cases, and is very useful for the brain and embryo preparations. 



26. Embryo Cords. (a.) Harden the spinal cord of an embryo chick at the 

 9th day as above. Remove as much as possible of the surrounding vertebral 

 column before placing it in the osmico-bichromate mixture. 



(L) Observe the axis-cylinders of the fibres of the anterior roots springing 

 from the axis-cylinder processes of the multipolar branch cells of the anterior 

 cornu, themselves black. Note that the fibres of the posterior root enter the 

 cord and split up into fibrils. 



(b.) Collateral Fibres. Harden the spinal cord of an embryo mammal (e.g., 

 sheep, 20-25 cm. long) or embryo of chick in the above fluid, and make L.S. 

 in the line of entrance of the posterior roots. The sections need not be very 

 thin, but one may have to make several preparations before one gets a satisfac- 

 tory result. 



(H) Note that when a fibre of the posterior root enters the white matter 

 of the cord it divides, sending one branch upwards and one dowmvards (fig. 

 322), which run for a distance more or less longitudinally, but many enter the 



1 Archiv. ital. de Biologic, xv. p. 462, 1891. 



* Internat. Monatsch. f. Anat. u. Phys., vi. p. 170. 



