SPECIAL STAINING METHODS 665 



fluid, which should not become turbid, nor should its odor of 

 osmium tetroxid entirely disappear. 



2. Rinse quickly in water. 



3. Place tissues in the silver solution, diluted with two volumes 

 of distilled water, for fifteen minutes. 



4. Place in the undiluted silver solution twenty-four to forty- 

 eight hours. If several pieces of tissue are prepared they should be 

 removed at intervals, as the duration of the impregnation by silver 

 is always an experiment. 



5. Dehydrate in absolute alcohol, one hour. 



6. Transfer to equal parts of absolute alcohol and ether, half an 

 hour. 



7. Thin celloidin (number 1), thirty minutes. 



8. Thick celloidin (number 3), thirty to forty-five minutes. 



9. Transfer to a wooden block and fasten with celloidin. 



10. Harden the celloidin block in chloroform, one-half to one 

 hour. 



11. Cut at once, the sections being 50 ft to 100 ft thick. While 

 cutting, the knife should be well moistened with bergamot oil, not 

 alcohol, and the sections, if not mounted at once, may be preserved 

 for a short time in the same oil. Oil of lavender, cajuput, or origa- 

 num may be used in a similar manner. 



Nitrate of Silver. This reagent is used to outline epithelial 

 cells by blackening the intercellular substance, the silver, after 

 impregnation, being reduced or blackened by exposure to light. 



1. The fresh tissue is immersed in a 0.25 per cent, to 0.5 per 

 cent, aqueous solution of silver nitrate (crystals), and left in the 

 dark for ten to twenty minutes. 



2. Wash in distilled water, and while still in water, expose to 

 direct sunlight until the object becomes a dark reddish-brown 

 color (ten to thirty minutes). 



3. Transfer to 70 per cent, alcohol, three to twelve hours. 



4. Preserve in 95 per cent, alcohol. 



Since nitrate of silver will attack metal instruments, the tissues 

 while in this solution should be handled with glass rods. In silver- 

 ing serous membranes, it is well to slightly stretch the object by tying 

 it over a cork with a thread tightly fastened around the edge. 



Gold Chlorid. 1. Wash the tissues in normal saline solution, 

 and place them in pure lemon -juice until they appear clear (five to 

 ten minutes). 



2. Wash quickly in distilled water. 



