G. Carl Huber 51 



neuroglial- tissue, partially interrupted by the appearance of Weigert's 

 large monograph, because the Weigert method did not seem to possess 

 the certainty ascribed to it by its discoverer. I am not aware that 

 Benda is familiar with the fact that his method may be used as a differ- 

 ential staining method for the neuroglia of animals. I find, however, 

 no reference to this fact in his account of his method. This fact seems 

 to me, however, of sufficient importance to warrant my giving his meth- 

 od somewhat in detail, since it does away with one of the obstacles to 

 the use of the Weigert or Mallory method— namely, the necessity of 

 using fresh human tissue in order to study the neuroglia with a differ- 

 ential stain. 



The method used by me in my study of the neuroglia of animals is 

 essentially the same as the first of the three methods given by Benda. 

 I have not been successful in staining the neuroglia of animals by the 

 other methods given by him. 



The method as used by me is as follows : ' 



1. The tissues, which should be in small pieces, not more than 

 0.5 cm. in thickness, are fixed and hardened for two to four days in a 

 4^ or 10^ solution of formaldehyde (10 parts or 25 parts respectively 

 of formalin in 100 parts of water). A large quantity of the solution 

 is used and, during the hardening process, the tissues rest on several 

 layers of filter paper placed in the bottom of the dish. 



3. The tissues are then placed for two to four days in Weigert's 

 chrom-alum mordant, used in his neuroglia stain, the solution being 

 kept in the warm oven at 38° C. during this step. 



3. Wash in flowing water for 24 hours. 



4. Place tissues for two to four days in a 0.5;^ aqueous solution of 

 chromic acid. 



5. Wash for 24 hours in flowing water. 



6. Dehydrate in graded alcohol. It is necessary to dehydrate the 

 tissues very thoroughly. 



7. Imbed in parafiin. It is necessary that this procedure be very 

 carefully carried out. After dehydration the tissues are placed in 

 xylol for 24 hours, renewing the xylol several times; then place them 

 for 12 hours in toluol and again 12 hours in benzole. Eenew the ben- 

 zole and add an equal quantity of melted soft paraffin and place in the 

 warm oven. At the end of 24 hours the mixture of benzole and paraffin 

 is replaced by soft paraffin and in three to four hours by hard paraffin 

 (58° C. melting point, Grlibler); after three hours' stay in this, they 

 may be imbedded. 



