44 2 THE CENTRAL NERVOUS SYSTEM. 



For thick sections the modified Weigert method, or Pal's method, 

 is employed. After the specimens have been treated according to Wei- 

 gert's method up to the point of staining with hematoxylin, they are placed 

 for from twenty to thirty minutes in a 0.25% solution of potassium per- 

 manganate. As differentiating fluid a solution of oxalic acid i gm., 

 potassium sulphite i gm., and water 200 c.c. is used, care being taken, 

 as in the case of Weigert' s differentiating fluid, that the gray matter is 

 thoroughly bleached (here entirely colorless) and the white matter dark. 

 By this method the medullary sheaths are stained blue, while the rest of 

 the structure remains colorless. The staining is very precise, but not so 

 intense as by Weigert' s method. Hence its adaptability for thicker 

 sections. 



Benda's method is a modification of the Weigert-Pal methods. The 

 tissues are hardened in Miiller's or Erlicki's fluid, imbedded in celloidin, 

 and cut. The sections are then subjected to the action of the following 

 mordant for from twelve to twenty-four hours : liquor ferri ter sulphatis 

 i part, distilled water 2 parts. They are then thoroughly rinsed in two 

 tap-waters and one distilled water and then stained in the following hem- 

 atoxylin solution: hematoxylin i gm., absolute alcohol 10 c.c., distilled 

 water 90 c.c.; in which they remain for twenty-four hours. They are 

 next washed in tap -water for from ten to fifteen minutes and treated with 

 a 0.25% aqueous solution of permanganate of potassium until the gray 

 and the white matter are differentiated, after which they are rinsed in 

 distilled water and bleached in the following solution until the gray mat- 

 ter has a light yellow color : hydric sulphite 5 to 10 parts, distilled water 

 100 parts. The sections are then washed in tap -water for from one to two 

 hours, rinsed in distilled water, dehydrated, cleared in carbol-xylol, and 

 mounted in balsam. Medullary sheaths will be stained a bluish-black ; 

 other structures, a light yellow. Sections stained after the Weigert, Pal, 

 or Benda method may be counterstained in Van Gieson's picric-acid- 

 fuchsin stain (i% aqueous solution of acid fuchsin, 15 parts; saturated 

 aqueous solution of picric acid, 50 parts ; distilled water, 50 parts) . 

 The fibrous connective tissue in the sections and degenerated areas stains 

 a light red. 



Apathy (97) demonstrates the fibrillar elements of the nervous 

 system in invertebrates and vertebrates by means of his gold method. 

 Fresh tissue may be used, or tissue already fixed. In the first case thin 

 membranes are placed for at least two hours in a i <f solution of yellow 

 chlorid of gold in the dark, then carried over without washing into a i % 

 solution of formic acid (sp. gr. 1.223), an d finally exposed for from 

 six to eight hours to the light (the formic acid may have to be changed). 

 These specimens are best mounted directly in syrup of acacia or in con- 

 centrated glycerin. In his second method Apathy fixes vertebrate tissues 

 for twenty-four hours in sublimate-osmic acid (i vol. saturated solution 

 of corrosive sublimate in 0.5% sodium chlorid solution combined with i 

 vol. 1% osmic acid solution), washes repeatedly in water, and places for 

 twelve hours in an aqueous iodo-iodid of potassium solution (potassium 

 iodid i Jc and iodin 0.5%). The further treatment is the same as after or- 

 dinary corrosive sublimate fixation. Finally,' the specimens are imbedded 

 in paraffin with the aid of chloroform, cut, and mounted by the water 

 method. The whole process, up to the point of imbedding in paraffin, 

 is carried out in the dark. The sections are then passed through chloro- 



