488 NEUROGLIA AND SENSE ORGANS. 



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



a fixing bath consisting of 



Concentrated solution of sodium hyposulphite 5 c.c. 



Distilled water 70 



Alcohol 30 



Concentrated solution of sodium bisulphite . 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. 



To ensure successful results the following points should be borne 



in mind : (1) The gold chloride must be of the brown variety. 



Its solution remains unaltered for months if kept in the dark. 



(2) The solution of mercury chloride becomes very easily altered, 

 and is best prepared when required, dissolving it with the help of 

 some heat, and filtering before adding it to the gold chloride solution. 



(3) 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 up 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. 



(4) More diluted gold baths may be used for economical reasons, 

 but in this case one must have recourse either to higher temperatures 

 or to greater lengths of time. (5) To proceed quicker, one may 

 either double the proportion of sublimate in the formula given above 

 or double the proportion of gold chloride and treble that of sublimate. 

 (6) 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 : 1000 solution of erythrosin or a minute quantity of the dry 

 dye, enough to impart to the bath a slightly orange tone. (7) 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 

 two months of hardening. Generally, the capacity for taking the 

 gold disappears first from the protoplasmic, and then from the 

 fibrous, neuroglia. 



