NEUROGLIA AND SENSE ORGANS 551 



after this time they are for some months in a condition particularly 

 suitable for the staining of the fibrous neuroglia. But if the time 

 of fixation is limited to one or hvo days at the temperature of 

 about 35° C, or to hoo up to four days at room temperature, the 

 tissues are in a state favourable to the impregnation of Cajal's 

 " third element " (§ 1093), which Del Rio-Hortega proposes to 

 term either microglia or mesoglia, the first of these two denomina- 

 tions being simply used with reference to the smallness of the 

 elements thus named, the second implying that they do not belong 

 to the neuroglia as this term is understood by Cajal and his 

 pupils. For the staining one may choose one or the other of the 

 following three processes : — • 



Process I, for protoplasmic and fihrous neuroglia. Sections 

 made by the freezing method are washed in two or three changes 

 of distilled water and transferred into a crystallising basin con- 

 taining 5 or 10 c.c. of ammoniacal silver carbonate solution, 

 prepared as follows : — To 50 c.c. of 10 per cent, silver nitrate 

 an equal or greater quantity of cold-saturated lithium carbonate 

 solution is added, so as to precipitate all silver in the form of 

 silver carbonate. The fluid part is poured off, and the precipitate 

 first washed with 200 to 300 c.c. of distilled water, and then 

 taken up with about 50 c.c. of diluted ammonia, by means of 

 which it is entirely dissolved. The solution is diluted with 

 distilled water up to a total volume of 250 c.c. and poured into a 

 dark brown bottle, where it keeps indefinitely, if put away in 

 some dark place. 



The crystallising basin, with the ammoniacal silver carbonate 

 and the sections placed therein, is warmed, either in an incubating 

 stove at 45° to 50° C. or over a flame, vmtil the sections become a 

 greyish-yellow colour. This requires only a few minutes if the 

 sections are moved about so that they may stain uniformly. 

 Good results may be also obtained by staining at 35° C. for twelve 

 to fourteen hours or at room temperature for one or two days. 

 Without waiting for the silver solution to become cool, the sections 

 are quickly washed in distilled water and then transferred, one 

 by one, into 20 per cent, formalin neutralised with chalk. After 

 one or two minutes, the reduction is complete, and the sections 

 may be washed, toned, fixed and dehydrated, cleared with a 

 mixture of carbolic acid 5 parts, xylol 45 parts, creosote 50 parts, 

 and mounted in balsam. 



Process II, for microglia. Sections are made as above, and 

 then treated for ten or fifteen minutes at 50° or 55° C. with the 

 bromide-formalin solution used for fixing. After washing in two 

 or three changes of water, one continues as in Process I, but 

 warming the ammoniacal silver carbonate solution at 50° or 

 55° C. until the sections are dark yellow. 



Process III, also for microglia. The pieces are warmed for 



