NERVE FIBER DEGENERATION 165 



NERVOUS SYSTEM 



2. To examine by polarized light 

 (Weaver, H. M., J. Lab. & Clin. Med. 

 1940-41, 26, 1295-1304). Lay excised 

 nerves without stretching on piece of 

 wooden tongue depressor and fix 24 

 hrs. or more in 10% neutral formalin. 

 Cut longitudinal frozen sections 10 

 microns thick. Float them onto slides 

 from water, mount in neutral glycerin 

 and examine. Weaver gives diagrams 

 to aid in interpretation of findings. See 

 also Pritchett, C. O. and Stevens, C, 

 Am. J. Path., 1939, 15, 241-250; Rad- 

 hakrishana, Rao, M. V., Ind. J. Med. 

 Res., 1938, 26, 103-106. 



3. To demonstrate early changes in 

 the axis cylinders (cores of the fibers) 

 Alzheimer's modification of Mann's 

 eosin-methyl blue method is strongly 

 recommended by Mallory as showing 

 normal axis cylinders deep blue and 

 degenerated ones, red. 



Nerve Fibers. Many excellent methods 

 present themselves : the continuous 

 direct observation of the growth of 

 individual fibers in living tissues of 

 lower animals (Speidel, C. S., Biol. 

 Bull., 1335, 68, 140-161); the micro- 

 dissection of living fibers (De Renyi, 

 G. S., Cowdry's Special Cytology, 1932, 

 3, 1370-1402) ; x-ray diffraction studies 

 of the sheaths (Schmitt, F. O., Bear, 

 R. S. and Palmer, K. J., J. Cell, and 

 Comp. Physiol., 1941, 18, 31-42) and 

 microincineration (Scott, G. H., Proc. 

 Soc. Exp. Biol. & Med., 1940, 44, 397- 

 398). For their demonstration in fixed 

 tissues consult methods of Bodian, 

 Davenport, Golgi, O'Leary, Osmic 

 Acid, Weigert and Weil. The methylene 

 blue technique of staining nerve fibers 

 is given under Auerbach's Plexus. 

 See Nerve Endings, Motor End Plates, 

 Bouton Ternxinaux. Use of quartz rod 

 illuminator in study of living nerve 

 fibers is described bv Speidel, C. C, 

 J. Comp. Neurol., 1935, 61, 1-80 and by 

 Bensley, S. H., Anat. Rec, 1944, 90, 

 1-11. 



Nerve Grafts, methods, histological and 

 otherwise (Sanders, F. K., and Young, 

 J. Z., J. Anat., 1942, 76, 143-166). 



Nerve Plexuses, see Auerbach's. 



Nerves. A red lead and carpenter's glue 

 method for injection and visualization 

 of blood vessels of nerves (Epstein, J., 

 Anat. Rec, 1944, 89, 65-69). Sec Pia 

 Mater perivascular nerves. 



Nervous System. This, the most compli- 

 cated of bodily parts, can be investi- 

 gated microscopically in a great many 

 different ways. It is however shielded 

 from the environment so that there are 

 great obstacles in the way of direct 

 observation in vivo. In mammals the 

 best that can be done is to insert win- 



dows in the wall of the skull. A 

 technique for this purpose, designed by 

 Forbes (H. S., Arch. Neurol, and 

 Psychiat., 1928, 19, 75), permits direct 

 study at low magnification of blood 

 vessels with so little injury that their 

 behavior in various experimental condi- 

 tions can be investigated. It is likely 

 that by the Sandison Technique very 

 significant observations can be made 

 on living, growing nerve fibers of the 

 rabbit. In amphibia Speidel (C. S., 

 Biol. Bull., 1935, 68, 140-161) has been 

 particularly successful in devising 

 methods for study of nerve fibers 

 in vivo. 



Another group of techniques is avail- 

 able for marking in vivo and examination 

 of the tissues after removal. Vital 

 Staining has been much used. Some 

 factors that condition the coloration of 

 nerve cells with trypan blue have been 

 described by King, L. S., J. Anat., 

 1934-35, 69, 177-180. The pathways 

 of drainage of cerebrospinal fluid can 

 be marked with Prussian Blue (Weed, 

 L. H., J. Med. Res., 1914, 26, 21-117). 

 Nerve fibers and cells can of course be 

 marked by the in vivo creation of in- 

 juries and subsequently examined. To 

 determine the distribution of Radio- 

 phosphorus may prove helpful. 



For the examination of excised tissues 

 a host of methods present themselves. 

 Consider first the classical techniques 

 from which several others spring. 



1. The original Nissl method for 

 internal structure of the nerve cell 

 consisted of fixing in alcohol and of 

 staining sections with methylene blue. 

 It revealed a basophilic material called 

 Nissl Substance. The unfortunate ten- 

 dency now-a-days is to loosely designate 

 all methods intended to demonstrate 

 this substance as Nissl techniques even 

 though resemblance to the original 

 method is lacking. 



2. The original Golgi method for the 

 external form of nerve cells depends 

 upon preliminary mordanting of tissue 

 in potassium bichromate solutions, fol- 

 lowed by immersion in weak aqueous 

 silver nitrate, and the cutting of thick 

 sections in which occasional nerve cells 

 and processes are outlined with startling 

 clarity by the black deposit of silver 

 chromate. Cajal modified and speeded 

 up the technique by addition of osmic 

 acid to the bichromate solution (see 

 Golgi Method, quick). But the most 

 used modification is the Golgi Cox 

 technique. 



3. The original Weigert method for 

 myelin sheaths of nerve fibers depended 

 likewise upon preliminary mordanting 

 in bichromate and the formation of 



