APPENDIX. 427 



Even in successful preparations only a limited number of cells 

 will be well shown ; this, however, is rather an advantage than 

 otherwise, since diagrammatic pictures are obtained of the various 

 elements in turn. The method is an impregnation, not a true stain, 

 defining outline, but not histological structure. The method is 

 also applicable to the demonstration of minute canals, as the bile 

 capillaries and glandular ducts. 



Golgi's gold method is useful for displaying naked axis-cylinders 

 and ultimate nerve-fibrillse, as well as special nerve-endings : the 

 method possesses the advantage of being relatively certain and rapid 

 in its action, especially if the reduction be facilitated by heat. 



Soak the fresh tissue in 



a. Arsenious acid .5 gm. 



Water, distilled 100 c.c. 



until it becomes translucent usually 1525 minutes. 



b. Transfer 



Gold chloride .5 gm. 



Water, distilled 100 c.c. 



for 25 to 45 minutes ; rinse off in distilled water. 



c. Transfer to i per cent, arsenious acid solution and expose to 

 sunlight until reduction follows and the tissue appears of a deep 

 purple or red color ; this reduction may be hastened by gently heat- 

 ing over water-bath for some 10 to 15 minutes, until the tissue be- 

 comes deeply colored. 



d. Wash thoroughly in water. 



e. Transfer to alcohol for dehydration, or to 50 per cent, glycerin, 

 as the case may demand respectively for balsam or glycerin mounting. 



Silver staining is an important means of bringing to view the 

 boundaries of epithelial and endothelial cells by the deposit of reduced 

 silver particles within the intercellular cement-substance ; in the typical 

 silver staining only the cell boundaries are shown as dark brown or 

 black lines, the protoplasm being almost colorless. In intensely 

 stained specimens of very fresh still living tissue the protoplasm and 

 nuclei are sometimes colored. The silver method also tinges the 

 interfibrillar ground-substance of dense connective tissue, bringing 

 to view the cell-spaces as clear areas within a colored field. 



The absolutely fresh tissue is carefully rinsed in distilled water, 

 without rubbing the surfaces, and then transferred to .5-1 per cent, 

 solution of silver nitrate from 2 to 10 minutes, depending on the 

 thickness of the object ; the then milky tissue is washed and exposed 



