XT AIMING. 395 



been stained, the sections may be mounted directly in Canada 

 balsam. If it is necessary to stain the sections, they should be 

 transferred from xylol to absolute alcohol. Since most of the 

 stains are aqueous solutions, the sections should be passed 

 through 95 per cent, and 45 per cent, alcohol before being 

 washed with water and placed in the staining fluid. If they 

 are transferred directly from absolute alcohol to water, there is 

 danger of their being loosened from the slide. 



(g) Staining. 



The object of staining tissues is to bring out more clearly 

 the details of their structure. As has been explained in the 

 section on the Blood, many stains can be divided into three 

 groups: the acid, the basic, and the neutral stains. The acid 

 stains color in general the protoplasm of the cells, while basic 

 dyes stain the nuclei. This affinity of special parts of the cell 

 for certain stains is the basis of what is known as differential 

 staining. In the commoner examples of this, the nucleus is 

 stained one color, and the protoplasm another. Other stains 

 have a special affinity for tissues or parts of tissues. These are 

 called specific stains (e. g., neuroglia stain, elastic tissue stain, 

 etc.). Tissues may be stained before they are sectioned, or 

 the sections themselves may be stained. 



The most useful stains in general laboratory work are men- 

 tioned briefly here, while the stains used for special purposes 

 are spoken of in the section on Special Technique. 



Carmine. This serves well for staining tissues before they 

 are cut. The alcoholic borax carmine of Grenadier is one of 

 the best solutions. It is made as follows: In 100 cc. of a 4 

 percent, aqueous borax solution there are dissolved by boiling 

 23 grammes of carmine; 100 grammes of 70 per cent, alcohol 

 are added, and after standing for a considerable time the solu- 

 tion is filtered. The already hardened pieces of tissue aiv 

 placed in this filtered solution for from one to three days. 

 From tli is they are transferred to acid alcohol (4-6 drops of 

 HC1 in 100 cc. of 70 per cent, alcohol), in which a differen- 

 tiation takes place. The stain remains in the nuclei, and is 



