NERVOUS SYSTEM 



166 



NEUROFIBRILS 



hematoxylin "lakes" when the sections 

 were later stained with hematoxylin. 

 Its most important modification is 

 known as Weigert-Pal. The Marchi 

 method, as modified by Swank and 

 Davenport is based on similar mordant- 

 ing with bichromate after which they 

 are treated with osmic acid and was 

 designed to reveal degenerated myelin 

 sheaths the lipids of which are unaf- 

 fected by the mordanting and are 

 blackened while those of the normal 

 sheaths are not. 



4. Cajal and Bielchowsky introduced 

 valuable methods for axones, neuro- 

 fibrils, and nerve eyidings including 

 synapses. Both techniques as applied 

 to blocks of tissue depend on preliminary 

 "silvering" with weak silver nitrate 

 solution but in those of the former the 

 silver is reduced by a photographic 

 developer generally hydroquinone or 

 pyrogallic acid; while in those of the 

 latter the tissues are first brought into 

 an ammoniacal silver solution and then 

 reduced in formalin. The most useful 

 modification is the Bodian Method 

 of activated protargol. See its evolu- 

 tion under Silver Methods which are 

 of assistance in the study of many 

 other tissues of the body as well as the 

 nervous system. 



5. Weigert's neuroglia stain was also 

 a classic, likewise Cajal's gold chloride 

 and sublimate method (1913) which 

 was soon followed bj'' Hortega's car- 

 bonate silver method (1917) . See recent 

 techniques under Neuroglia. 



There are still other techniques to 

 choose from which are not so directly 

 developments of the neurological 

 classics. Nerve cells are closely mixed 

 with fibers. To isolate them sufficiently 

 for direct study at high magnification 

 in approximatelj'' isotonic media in- 

 volves considerable injury and they 

 cannot be held under observation for 

 long periods because their death ensues 

 fairly quickly. Spinal ganglion cells 

 are the easiest studied. The Macera- 

 tion technique is not much used for the 

 nervous system but Addison (McClung, 

 p. 439) states that, if pieces of the 

 anterior horn of the spinal cord are 

 treated with Gage's dissociator (0.2% 

 formalin in physiological saline) for 

 2-3 days, the nerve cells can easily be 

 dissected out under a binocular micro- 

 scope, stained and examined more or 

 less as units. Tissue Culture of nerve 

 cells of the adult is not feasible because 

 they are fixed postmitotics (having 

 permanently lost the power of multi- 

 plication) ; but culture of young tissues 

 provides interesting results (Levi, G., 

 Arch, de Biol., 1941, 52, 1-278, profusely 

 illustrated). Nerve Fibers are more 



easily isolated and their investigation 

 in the fresh state is very profitable. 

 The histological localization of Cho- 

 linesterase is now feasible. The meas- 

 urement of oxidative metabolism in dif- 

 ferent parts of the nerve cell by 

 reduction of ferric chloride (Gerard, 

 R. W., Assoc, for Res. in Nerv. & Ment. 

 Dis., Baltimore, Williams & Wilkins, 

 1938, 18, 316-345) can probably be tied 

 up with localization of Oxidases and 

 Peroxidases. Marinesco (G., Arch. 

 Suisse de Neurol, et de Psych., 1924, 

 15, 1-24) has published repeatedly on 

 these enzymes in nerve cells. Methods 

 for Pigments and Lipids can easily be 

 applied to the nervous system. For 

 microincineration of nerve cells and 

 fibers see Scott, G. H., Froc. Soc. Exp. 

 Biol. & Med., 1940, 44, 397-398. If it is 

 desired to demonstrate mitochondria 

 the Anilin-Fuchsin Methyl Green 

 method is suggested after fixation by 

 vascular perfusion plus immersion. See 

 in addition to above headings : Auer- 

 bach's Plexus, Axis Cylinders, Boutons 

 Terminaux, Centrosomes, Cresyl Violet, 

 Golgi Apparatus, Microglia, Motor 

 End Plates, Nerve Endings, Neuro- 

 fibrils, Neurosecretory Cells, Oligo- 

 dendroglia. 



Neufeld's Quelling Reaction. This is a 

 microscopicaliy demonstrable swelling 

 of the capsules of pneumococci which is 

 of distinct value in typing (L. W. Parr, 

 in Simmons and Gentzkow, p. 426). 



Neumann's Crystals, sec Charcot-Leyden. 



Neurofibrils. These delicate fibrils and 

 networks can be demonstrated with 

 difficulty mainly by methods of silver 

 impregnation in the cytoplasm of nerve 

 cells. In the living nerve cells of 

 selected invertebrates they can also be 

 seen but opinion is divided as to whether 

 tiiey can be detected in the living nerve 

 cells of vertebrates (Cowdry, p. 393). 

 None of the techniques for neuro- 

 fibrils are really satisfactory, but, with 

 patience, fairly good results can be 

 secured of adult nerve cells by the 

 following modification (Cowdry, E. V. 

 Internat. Monatssch. f. Anat. u Phy- 

 siol., 1912, 29, 1-32) of Cajal's technique. 

 Fix pieces not more than 2 mm. thick 

 in Carnoy's 6:3:1 fluid 2-6 hrs. Wash 

 in aq. dest. 24 hrs. 1.5% aq. silver 

 nitrate at 39 °C. for 3 days with one 

 change. Rinse in aq. dest. and reduce 

 in pyrogallic acid 1 gm.; aq. dest., 100 

 cc; formalin 5 cc. in the dark, 24 hrs. 

 Wash in aq. dest. 1 hr. Dehydrate 1 

 hr. in 95%; 2-4 hrs. in abs. changed 

 twice; clear in cedar oil, 2 hrs.; imbed 

 in paraffin 2 hrs. Rinse deparaffinised 

 sections in aq. dest. 0.1% aq. gold 

 chloride neutralized with lithium car- 

 bonate 2 hrs. The sections take a dark 



