492 NEUROGLIA AND SENSE ORGANS. 



0-2 per cent, gold chloride ; fix, wash, dehydrate and mount as 

 usual. 



921. DEL RIO-HORTEGA'S Carbonate of Silver Method (Trab. Lab. 

 Invest. BioL, Madrid, xv, 1918, and xvii, 1920 ; Bol. Soc. Esp. BioL, 

 viii, 1918). Pieces of quite fresh nervous tissues are fixed in Cajal's 

 ammonium bromide-formalin mixture, and kept therein for different 

 periods of time, according to the purposes in view. If it is desired 

 to stain the protoplasmic neuroglia, pieces are best fixed for twenty 

 to thirty or forty days ; 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 two days 

 at the temperature of about 35 C., or to two up to four days at room 

 temperature, the tissues are in a state favourable to the impregnation 

 of Cajal's " third element " ( 919), 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. 

 See 919. For the staining one may choose one or the other of the 

 following three processes :- 



Process I, for protoplasmic and fibrous neuroglia. - - Sections 

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

 of distilled water and transferred into a crystallising basin 

 containing 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, until 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 



