260 S. WALTER RANSON 



TECHNIQUE 



The spinal cord of the cat forms very favorable material to 

 which to apply the pyridine-silver technique. Preparations ob- 

 tained from the cords of other laboratory animals (dogs, rabbits, 

 guinea-pigs and rats) are not so perfect. 



Under anaesthesia the animals were exsanguinated. The spinal 

 cord was exposed and the ganglia on the C^ C^, T^ T*, T^-, L^, 

 and S^ spinal nerves were dissected out and left attached to 

 their respective segments of the spinal cord. These segments 

 with their associated roots and ganglia were then removed and 

 freed from dura. Preparations were made by the Pal-Weigert 

 as well as the pyridine-silver method. For the latter the pieces 

 were not more than 5 mm. long, and after the usual treatment 

 (Ranson '11), were imbedded in paraffin and cut into sections 

 varying from 8 to 12 ^ in thickness. Serial sections of a number 

 of levels were mounted, to trace more in detail the entering 

 bundles from the roots. The Pal-Weigert material was cut in 

 celloidin into sections of 12 /^ and 24 /x thickness. Usually sections 

 of both thicknesses were cut from each segment. The technique 

 of the silver stain has already been published (Ranson '11 and 

 '12) and the Pal-Weigert method needs no explanation. 



Structure of the substantia alba of the spinal cord 



Cajal's silver method and its various modifications are known 

 to give instructive preparations of the gray substance of the 

 nervous system. In the preparations of the spinal cord of the 

 cat it is superbly stained, showing the greatest detail in the peri- 

 cellular fiber plexuses, and the endocellular fibrillar reticulum. 

 It is, however, in the fiber columns of the cord that the pyridine- 

 silver preparations present the most interesting differentiation. 

 As in the peripheral ner\'es, the axons of the medullated fibers 

 stain a light yellow and are surrounded by unstained rings of 

 myelin; while the non-medullated axons are dark brown or black. 

 Areas consisting chiefly of medullated fibers appear light yellow 

 under low magnification because of the predominance of light 

 yellow axons and unstained myelin. Other areas are lighter or 



