CHAPTER XXXV. 



NEUROGLIA, AND SENSE ORGANS. 



Newroglia. 



837. INTRODUCTION. Nenroglia cells may be isolated by 

 teasing, and may be stained in many ways (see RANVIER, 

 Traite.j p. 1063), by osmic acid, nigrosin, carmine, orcein. 

 Iron haematoxylin is said to give good results with the lower 

 vertebrates. (I have not found it so.) But by far the best 

 method for the study of the forms and relations both of 

 ependyma cells and astrocytes is the Bichromate -and- silver 

 Impregnation of GOLGI, the best material being that which 

 has been for not more than two or three days in the osmio- 

 bichromic mixture. 



This method, however, does not tinctorially differentiate 

 between neuroglia-cells and nerve-cells, and is of no use for 

 mapping out tracts of neuroglia as a whole. The following 

 methods are intended for this. They either stain neuroglia 

 more or less specifically, leaving other tissues unstained 

 (WEIGERT), or stain it in a different tone to other tissues. 

 None of them are satisfactory. WEIGERT'S process stains the 

 processes of the cells (his " fibres ") intensely, whilst leaving 

 the cell-body unstained ; and in consequence, if exclusively 

 followed, may lead to erroneous conclusions. 



838. WEIGERT'S Neuroglia Stain (WEIGERT'S Beitr. zur 

 Kenntniss der normalen menschlichen Neuroglia, Frank furt- 

 a-M., 1895; and his art. " Ncurogliafdrbung* in Encycl. 

 MiJf. Technik).- Pieces of very fresh tissue of not more than 

 half a centimetre in thickness are put for at least four days 

 into 10 per cent, formol. They are then mordanted for four 

 or five days in an incubating stove (or for at least eight days 

 at the temperature of the laboratory) in a solution containing 



