494 NEUROFIBRILS 



through xylol and acetone into distilled water ; silver for three days at 

 about 37° C. in 20 per cent, solution of silver nitrate. Put for ten minutes 

 into a mixture (at least three days old) of 1000 parts of water, 10 of 

 sodium acetate, 5 of gallic acid, and 3 of tannin (to be changed if it 

 becomes turbid). Mount at once or tone until grey (five minutes) in 

 80 parts of water with 17 of 2 per cent, ammonium sulphocyanide and 

 3 of 2 per cent, gold chloride ; fix for a few seconds in 5 per cent, sodium 

 h5T)osulphite. Neurofibrils grey-violet, shown in cells, dendrites, and 

 axons. Terminal buds of Held also clearly shown, and nothing else 

 stained. One may counterstain in any way, even by Weigert's or 

 Benda's methods for neuroglia stain. 



Gros' method (see Romeis, " Taschenbuch der mikroskopischen 

 Technik," 12 auf. 1928 ; R. Olderbourg, Munchen u. Berlin) is 

 valuable, as by it staining of the connective tissue fibres can be avoided. 

 Denny-Brown, who has modified this method for use on celloidin material, 

 recommends the following technique : Celloidin sections up to 50 [x in 

 thickness are placed in distilled water for half to one hour to remove 

 all traces of alcohol. They are then transferred to 20 per cent, silver 

 nitrate for one hour in the dark. Frozen sections are first treated with 

 pure pyridine or with alcohol for twenty-four hours and then washed 

 for two to three hours in distilled water until there is no odour of 

 pyridine in order to prevent staining of the myelin sheaths. In celloidin 

 imbedding passage though absolute alcohol suffices to overcome this 

 disadvantage, but if desired the material may be treated with pyridine 

 before imbedding. Sections are transferred from the silver bath, with- 

 out washing, to a 20 per cent, solution of formalin neutralised with 

 magnesivun carbonate and are left there until no further white cloud 

 appears, the solution being renewed two or three times. The reducing 

 solution is prepared by adding strong ammonia drop by drop to 5 to 

 15 c.c. of 20 per cent, solution of silver nitrate until the precipitate 

 which forms just disappears and then adding 1 small drop of ammonia 

 for each cubic centimetre of silver taken. The sections are washed 

 quickly in distilled water before this bath, but if the material proves 

 difficult to stain, try transferring a section or two without washing. 

 The reduction must be controlled under the low power of the microscope, 

 the reducing bath being poured into a small Petri dish or watch-glass 

 for the purpose. If nuclei and connective tissue begin to stain first, or 

 before the axis cylinders are fully stained, add a drop of ammonia to 

 the reducing bath. If no axis cylinders stain after ten minutes, add one 

 drop of 20 per cent, formol to the bath. Sections must be kept fully 

 immersed as evaporation of ammonia may cause overstaining of any 

 part of the section which comes to the surface. After staining, the 

 sections are placed in a 20 per cent, solution of ammonia for at least a 

 minute (five minutes for thick sections). They are then transferred to 

 1 per cent, acetic acid for the same length of time and subsequently toned 

 in 0-2 per cent, gold chloride, fixed in hyposulphite and washed in dis- 

 tilled water. They may be counterstained with van Gieson for a few 

 seconds or with J per cent, thionin or toluidin for a minute. They 

 may also be covmterstained with both iron haematoxylin and van Gieson 



if desired. 



Davenport {Arch. Neurol, and Psychiat., xxiv, 1930, p. 690) coats 

 celloidin sections from spirit with 2 per cent, celloidin after mounting 

 them on albuminised slides and then puts them into 80 per cent, alcohol 

 for a few minutes before placing the slides in a silver bath prepared by 

 dissolving 10 grm. of silver nitrate in 10 c.c. of distilled water, adding 

 90 c c. of 95 per cent, alcohol and 5 to 7 drops of approximately normal 

 nitric acid to each 50 c.c. of silver solution. The slides are left in the 

 silver bath until the sections are light yellow in colour (usually over- 



