546 NEUROGLIA AND SENSE ORGANS 



method, and collected in distilled water to which a few drops of 

 formalin have been added. After a quick wash, batches of four 

 to six sections are each transferred into glass dishes of about 6 cm. 

 in diameter, and each containing 15 c.c. of a mixture of — 



Distilled water . . . . .60 c.c. 



Mercuric chloride . . . .0-5 grm. 



1 per cent, gold chloride (Merck, brown 



variety) ...... 10 c.c. 



After about four hours the sections will be found to have become 

 an intense purple, and can be passed, for five to ten minutes, into 

 a fixing bath consisting of — 



Concentrated solution of sodium hypo- 

 sulphite ...... 5 c.c. 



Distilled water . . . . . 70 ,, 



Alcohol . . . . . . 30 ,, 



Concentrated solution of sodium bisul- 

 phite . . . . . . 5 ,, 



Wash in 50 per cent, alcohol, lift sections on to slides, dry with 

 filter paper, wash with absolute alcohol, clear with origanum oil, 

 wash with xylol, and mount in balsam. 



Best results are obtained by keeping the glass dishes, with the 

 sections and the gold chloride-sublimate mixture, at a temperature 

 of 18° to 20° C. If the reagent is freshly prepared, the reaction 

 will be complete in about four to six hours. At temperatures 

 between 14° and 17° C. three or four hours more are necessary 

 to obtain good stains. With temperatures below 14° or 12° C. 

 it is very difficult to obtain any reaction at all. One may have 

 recourse to temperatures above 20° C, up to 27° or 30° C. in 

 special cases, as Del Rio-Hortega has done for the neuroglia of 

 the pineal body. More diluted gold baths may be used for eco- 

 nomical reasons, but in this case one must have recourse either 

 to higher temperatures or to greater lengths of time. To proceed 

 quicker, one may either double the proportion of sublimate in 

 the formula given above or double the proportion of gold cliloride 

 and treble that of sublimate. A good means to obtain rapid 

 and vigorous reactions consists in adding to the gold chloride- 

 sublimate bath either 2 to 3 drops of a 1 : 100 solution of ery- 

 throsin or a minute quantity of the dry dye, enough to impart 

 to the bath a slightly orange tone. All other conditions being 

 the same, results are greatly influenced by the length of time 

 during which the pieces have been kept in the fixing fluid. As 

 a rule, they begin to be ripe for cutting from the end of the 

 third day, and they continue to be in a state favourable for 

 obtaining good reactions for another five or six up to fifteen or 

 twenty days. Good stains may be exceptionally obtained after 



