530 Journal of Applied Microscopy. 



while in the dorsal roots the number decreases from the ganglion toward the 

 spinal cord. This decrease occurs among the small fibrils and is explained as 

 being the natural result of the growth of nerve fibers. 



In growing frogs the fibrils of the dorsal root increase more rapidly than 

 those of the ventral root. Most of these fibrils go to innervate the skin and 

 there is probably some relation between this increase and the increase in the sur- 

 face of the skin. 



There are more fibers in the trunk and dorsal branches than there are in 

 both roots. This may be due to a splitting of the fibrils in the spinal ganglion, 

 or there may be cells in the ganglion which send a process to the peripher}^ but 

 not to the centrum, or the distal branch of a T-shaped fiber may become medul- 

 lated before the other branch, or there may be small medullated fibers from the 

 sympathetic system which end in the ganglion. 



Technique. — The cord and nerves were hardened /;/ situ with osmic acid, 

 washed, and then treated for one hour with a 5 per cent, aqueous solution of 

 pyrogallic acid to emphasize the blackening. Cross sections of nerves were 

 photographed, and when the fibrils were counted the section was compared with 

 the photograph. A specially designed automatic registering machine was used 

 for counting. e. m. b. 



Dollken, A. Weigert-Pal-Farbung sehr junger Sections are cut about 50// thick— 30/1 

 Gehirne. Zeit. f. wiss. Mikr., IS: 443-445, for rats or mice — and given the usual 



treatment for photoxylin plates after 

 Obregia. Stain in cold hematoxylin solution (Pal), for four or five days, then at 

 37° C. for two hours ; after cooling leave in spring water for six or eight hours, 

 without changing the water, and follow with alkaline distilled water (two or three 

 drops of potassium to a liter) for fifteen minutes. Decolorize in about one-half 

 per cent, potassium permanganate until the unmedullated parts begin to be 

 transparent. Wash thoroughly in distilled water, place in a one per cent, solu- 

 tion of oxalic acid until the unmedullated parts become light brown, and "the 

 nuclei darker, and follow this with a quantity of distilled water in which the sec- 

 tion will clear up still more. The fibers will be dark blue, the nuclei and 

 cortex light brown to yellow, undeveloped places light yellow to white. Single 

 steps should not be repeated. This is an especially delicate method for young 

 brains, and any carelessness may result in over-bleaching the fibers, and in 

 obscuring the contures of the ganglia and the nuclei. 



The stain may be used after chromic acid fixation, but gives especially good 

 results after a five or ten per cent, solution of formaldehyde. Material should 

 be left in this until the potassium chromate will produce no further shrinking — 

 at least fourteen days for a dog's brain, and from three to four weeks for a 

 child's brain. 



If chromic acid is used, from five to seven months are required. Thorough 

 fixation and uniform hardening are of the greatest importance. The method 

 demonstrates the form and arrangement of the ganglion cells as well as carmine, 

 and also shows the path of the fibers. e. m. b. 



