TECHNIC. 441 



rated solution of lithium bicarbonate (i. c.c. to 100 c.c. of hematoxylin 

 solution) brings out the staining power of the solution at once. In 

 this stain the sections are placed (at room -temperature) for a day, and 

 then in a thermostat (40 C.) for a few hours. The sections, now quite 

 dark, are washed in distilled water and then placed in the so-called dif- 

 ferentiating fluid. The latter consists of borax 2 gm., ferrocyanid of 

 potassium 2.5 gm., and distilled water 100 gm. In this fluid the color 

 of the sections is differentiated by virtue of the circumstance that the 

 medullary sheath retains the dark stain, while the remaining structures, 

 such as the ganglion cells, etc. , are bleached to a pale yellow. The time 

 required for this differentiation varies, but it is usually complete at the end 

 of a few minutes. The sections are then washed in distilled water, dehy- 

 drated in alcohol, cleared in carbol-xylol (carbolic acid i part, xylol 3 

 parts) and mounted in balsam. 



Weigert's new method is more complicated, but fruitful of cor- 

 respondingly better results. The preliminary treatment remains the same. 

 After the tissues have been imbedded in celloidin and this hardened in 

 80% alcohol, they are transferred to a mixture composed of equal parts 

 of a cold saturated aqueous solution of neutral copper acetate and 10% 

 aqueous solution of sodium and potassium tartrate, and the whole is placed 

 in the thermostat. Larger pieces as, for instance, the pons Varolii of 

 man may remain in the solution longer than twenty-four hours, after 

 which time, however, the mixture must be changed ; but in no case should 

 the specimens be permitted to remain longer than forty -eight hours in 

 this solution. The temperature in the thermostat should not be high, 

 otherwise the specimens will become brittle. The objects are now placed 

 in a simple aqueous solution of neutral copper acetate, either saturated 

 or half diluted with water, and again put in the oven. They are then 

 rinsed in distilled water and placed in 80 /o alcohol ; after remaining 

 in this for one hour, they are in a condition to cut, but may be preserved 

 still longer if desired. Cut and stain in the customary manner. The 

 staining solution is prepared as follows : (a) lithium carbonate 7 c.c. and 

 distilled water 93 c.c. (saturated aqueous solution) ; (Ji) hematoxylin i 

 gm., absolute alcohol 10 c.c. ; both a and b keep for some time, and may 

 be kept on hand as stock solutions. Shortly before using, 9 parts of a 

 and i part of b are mixed. After remaining in this solution for from 

 four to five hours at room-temperature the sections are well stained, but 

 do not overstain even if allowed to remain in the solution for twenty-four 

 hours. In the case of loose celloidin sections the use of the differentiat- 

 ing fluid is superfluous. Hence this method is particularly advantageous 

 when the gray and the white matter can not be distinguished macro- 

 scopically. Finally, the sections are washed in water, placed in 95% 

 alcohol, cleared with carbol-xylol or anilin-xylol (in the latter case 

 carefully washed with xylol), and mounted in xylol -balsam. The medul- 

 lated fibers appear dark blue to black, the background pale or light 

 pink, and the celloidin occasionally bluish. In order to remove the latter 

 color, it is only necessary to wash the sections in 0.5% acetic acid in- 

 stead of ordinary water ; a process, however, not to be recommended 

 in the case of very delicate preparations as, for instance, the cerebral 

 cortex. In applying Weigert's methods a certain thickness of section 

 (not exceeding 25 /*) is essential, since in thicker sections the medullary 

 sheaths are not sharply differentiated from the surrounding tissue. 



