

METALLIC STAINS GOLGI METHODS 33 



which become colored reddish brown. Eosinophile granules 

 become brilliant red. Nuclei are stained green by it, while the red 

 corpuscles are orange -red or brown. Its use will be referred to in 

 the chapter on blood. 



METALLIC STAINS OR IMPREGNATIONS 



Compounds of silver, gold, mercury, and osmium are used to 

 color particular elements in the tissue, or they are precipitated in 

 certain structures as opaque deposits. Osmic acid has already been 

 described on page 23. Of the other substances, NITRATE OP SILVER 

 is the most important. 



This salt is used in dilute solutions (1-300, 1-500) made 

 with distilled water. It is most valuable to stain the cement-sub- 

 stance between the endothelial cells of membranes, like the peri- 

 toneum. The membrane is stained while fresh, and must be 

 washed free of all albuminous substances which might precipitate 

 the silver. It should also be stretched over the rim of a dish. 

 The solution of nitrate of silver should be allowed to act upon the 

 membrane, care being taken to have it reach all parts of the 

 surface. It has little penetrating power. After five to ten minutes 

 wash in water, and expose to the sunlight, in which the color 

 becomes brown, owing to dark lines which develop between the 

 cells. Mount in glycerin or balsam. 



GOLGI METHOD FOR STAINING BRAIN AND SPINAL CORD 



There are many formulas which different investigators have 

 used with more or less success. All of them seek to impregnate 

 the tissue with silver or mercury salts, which become precipitated 

 on ome of the nerve-elements and render them visible. At best, 

 the Golgi method is uncertain, but when it is successful, the prep- 

 arations obtained are of great beauty and value. 

 The following procedure can be recommended : 

 a. Small pieces of fresh tissue are hardened from two days 

 to a week in 



Osmic acid, one per cent 10 c.c. 



Potassium bichromate, three and one -half per cent. 40 c.c. 



The time required varies according to the part of the tissue 

 to be stained. Neuroglia requires the shortest and nerve-fibers the 



c 



