444 THE CENTRAL NERVOUS SYSTEM. 



move the alcohol. The slides (with the sections fixed to them) are then 

 taken from the water and rinsed with distilled water from a water-bottle. 

 The slide is then wiped dry on its under surface and edges with a clean 

 cloth, and about i c.c. to 1.5 c.c. of distilled water placed on the slide 

 over the sections. The slides are now placed in a warm oven with a tem- 

 perature of 55 C. to 60 C. for a period of time varying from two to 

 ten minutes. No definite time can here be given ; sections from each 

 block of tissue need to be tested until the right stay in the warm oven is 

 ascertained. The slides are then taken from the warm oven and rinsed 

 two or three times in distilled water and again dried as previously 

 directed. They are then covered with the following staining solution 

 and again placed in the warm oven for about ten minutes : toluidin-blue, 

 i part ; distilled water, 3000 parts. The stain is washed off with dis- 

 tilled water and the sections are placed in 96% alcohol until no more 

 stain is given off usually for from three-fourths to two minutes. They 

 are then dehydrated in absolute alcohol, passed through xylol twice, and 

 mounted in xylol balsam. For a fuller discussion of this method the 

 reader is referred to Bethe's account in " Zeitsch. f. Wissensch. Mikrosk.," 

 vol. xvn, 1900. 



For staining neuroglia Weigert (95) has recommended a 

 method, from which we give the following : A solution is made consisting 

 of 5% neutral acetate of copper, 5% ordinary acetic acid, and 2.5% 

 chrome -alum in water. The chrome-alum and water are first boiled 

 together, the acetic acid then added, and finally the finely pulverized 

 neutral copper acetate, after which the mixture is thoroughly stirred and 

 allowed to cool. To this solution 10% formalin may be added. Objects 

 not over 0.5 cm. in diameter are placed in this fluid for eight days, the 

 mixture being changed at the end of a few days. By this means the 

 pieces of tissue are at the same time fixed and prepared for subsequent 

 staining by the action of the mordant. If separation of the two processes 

 be desired, the specimens are fixed for about four days in a 10% formalin 

 solution (which is changed in a few days), and then placed in the 

 chrome-alum mixture without the addition of formafin. Specimens thus 

 fixed may be preserved for years without disadvantage, and may then be 

 subjected to further treatment by other methods, Golgi's for instance. 

 Washing with water, dehydration in alcohol, and imbedding in celloidin 

 are the next steps. The sections are then placed for about ten minutes 

 in a 0.33% solution of potassium permanganate, washed by pouring water 

 over them, and placed in the reducing fluid (5% chromogen and 5% 

 formic acid of a specific gravity of 1.20; then filter carefully, and 

 add 10 c.c. of a 10% solution of sodium sulphite to 90 c.c. of the fluid). 

 The sections, rendered brown by the potassium permanganate, readily 

 decolorize in a few minutes, but it is better to leave them for from two to 

 four hours in the solution. If it be desirable to decolorize entirely the 

 connective tissue, no further steps need be taken preliminary to staining ; 

 if not, the reducing fluid is poured off and the sections are rinsed twice 

 in water and then placed in an ordinary saturated solution of chromogen 

 (5% chromogen in distilled water, carefully filtered). The sections are 

 left in this solution overnight, and the longer they remain in it, the more 

 marked will be the contrast, as far as stain is concerned, between the con- 

 nective and nervous tissues ; then water is again twice poured upon the 

 sections and they are ready for staining. This process consists in a 



