NEUROGLIA 



226 



NEUTRAL GENTIAN 



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 

 they 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 

 purple black color. 5% aq. sodium 

 hyposulphite 5 min. to bleach out 

 excess of silver. Rinse in aq. dest. 

 dehydrate, clear in toluol and mount in 

 balsam. 



The neurofibrils are exaggerated op- 

 tically by their sharp blue black stain 

 in a colorless background. Moreover 

 they form centers for the deposit of 

 silver which probably increases their 

 bulk. The Nissl bodies can be brought 

 out by staining in the usual way with 

 toluidin blue after washing in aq. dest. 

 following treatment of the sections with 

 sodium hyposulphite. The essential 

 step in this technique is the impregna- 

 tion with silver. Consequently the 

 time in the silver solution should be 

 varied and perhaps its concentration 

 likewise. To obtain a good preparation 

 without many trials is not to be ex- 

 pected. 



Silver techniques for neurofibrils are 

 legion. A book has been written on 

 the subject (Cajal, S. R. and deCastro, 

 F., Elementos de Tecnica micrografica 

 del sistema nerviosa. Madrid, 1933). 

 Special methods are advised for different 

 parts of the nervous system and for 

 animals of different sorts and ages. A 

 very useful synopsis is given by Addi- 

 son (McClung, 1950, p. 364). See also 

 Seki, M., Ztschr. f. Zellf. u. Mikr. 

 Anat., 1939-40, 30, 548-566. 

 Neuroglia. This is the connective tissue 

 of the nervous system. Like that of the 

 rest of the body it consists of cells, fibers 

 (or fibrils as they are called) and inter- 

 cellular substance. The last named is 



inconspicuous and little known. The 

 Neuroglia Fibrils are considered sepa- 

 rately. The cells are of three principal 

 sorts: (1) microgliocytes of mesenchy- 

 raatous origin. These may be resting 

 and extend long, delicate processes or 

 they may be ameboid in which case 

 they look something like lymphocytes 

 being usually identifiable by intensely 

 staining nuclei. (2) astrocytes (star 

 cells) and (3) oligodendrocytes (little 

 tree cells) both of ectodermal origin. 

 A tabular comparison of the three is 

 given in Cowdry's Histology, p. 406. 

 No neuroglial cells possess Nissl bodies. 

 See Cajal's Brom-Formol-Silver 

 Method, the Phosphotungstic Acid 

 Hematoxylin method of Mallory, Weil 

 and Davenport's silver methods given 

 under Microglia and Oligodendroglia 

 and Alzheimer's Modification of Mann's 

 eosin-methyl blue method. See, also 

 Silver Diaminohydroxide after sensitiz- 

 ing with sodium sulfite. 



Neurones, see Nerve Cells. 



Neurosecretory Cells. A good deal has been 

 written on the subject. The most 

 recent data on location in nervous 

 system and methods are provided by 

 Scharrer, E., J. Comp. Neurol., 1941, 

 74, 87-92; Scharrer, B., ibid, 93-130. 



Neutral Fats. These are glycerides of 

 fatty acids. See Lipids, examination 

 of with polarized light. Colored rose 

 red by Nile Blue Sulphate. See Sudan 

 Stains, Osmic Acid and Oil Red O. 



Neutral Gentian (Bensley, R. R. Am. J. 

 Anat., 1911, 12, 297-388). This gives a 

 very fine deep violet coloration of secre- 

 tion antecedents of serous (or zymo- 

 genic) cells. It has been used particu- 

 larly for the pancreas and the stomach. 

 Neutral gentian is the neutral dye 

 obtained when aq. gentian violet 

 (crystal violet) is precipitated by its 

 equivalent of aq. orange G which is 

 added slowly and the mixture agitated. 

 Use solutions almost but not quite satu- 

 rated. If the right amount of orange G 

 solution is added almost complete 

 precipitation is obtained. If too much 

 is added the precipitate is dissolved in 

 which case add more gentian violet. 

 Excess of orange G can be detected by 

 the production of a yellow ring of stain 

 about a violet center when a drop of the 

 solution with the precipitate is touched 

 to a piece of filter paper. When satisfied 

 that ppt. is maximal, filter; and dissolve 

 dried ppt. in 20% ale. until "color of a 

 good haemalum solution is obtained". 

 Allow the solution to stand 24 hrs. 

 before use. 



Fixatives: Several are advised. (1) 

 Equal parts sat. ale. mercuric chloride 

 and 2.5% aq. potassium bichromate. 



