CH. X] STAINING AND PERMANENT MOUNTING 311 



usually contrasting in color ; blue or purple and bright red are frequent com- 

 binations, e. g. hematoxylin and eosin. 



(2) From the standpoint of the solvent used in preparing the stains they 

 are called (a) sit/neons, and (b) alcoholic. 



If one uses an aqueous stain the object must be well wet with water before 

 the stain is applied, and afterward well washed with water before put again 

 into alcohol. If an alcoholic stain is used the object to be stained should be 

 from alcohol of the same strength as that used in making the dye. The dye is 

 also washed away from the tissue with the same strength of alcohol ; it may 

 then be put into the stronger alcohols for dehydration. 



For other classifications of dyes consult the larger works, Lee, Mann, 

 Ehrlich, and the microscopical journals. 



FIG. 250. Pipette with large rubber bitlb for adding liquids to prepara- 

 tions. (Cut loaned by the Bausch & Lomb Optical Co. ) 



\ 462. Generalities on Mounting. For permanent preparations one can 

 use a medium like glycerin or glycerin jelly etc. which mixes with water. 

 The method of procedure is given in \ 407, 408. 



For the most permanent mounting resinous media are used, and of these 

 resinous media Canada balsam ( 383) has been longest, and is now most used. 



In mounting in balsam one must remember the fundamental principles : 

 (i ) the object to be mounted in balsam must not contain water. It must then 

 be dried or desiccated, or it must be rendered anhydrous by some liquid which 

 mixes with water. As all tissues and organs contain much water, to mount 

 them in balsam without drying in the air, which would spoil them in most 

 cases, one must take the following steps ( i ) Dehydrate by alcohol which mixes 

 with and displaces the water; (2) Displace the alcohol by some liquid which 

 mixes with it and is also miscible with balsam, e. g. xylene, etc. ( 392). 

 (3) As the liquid used just before the balsam usually makes the tissue more or 

 less translucent it is often called a "clearer". Finally displace the xylene etc. 

 by balsam. If all the water is not removed in some way, the specimen will 

 look turbid. If there is but a trace of water present and one uses natural 

 balsam (? 383 ) for mounting the small amount of water will finally disappear; 

 but it is better to dehydrate the tissue thoroughly before adding the balsam. 



HEMATOXYLIN WITHOUT AND WITH COUNTERSTAINING 



^ 463. Staining with Hematoxylin. Take a slide of sections 

 prepared by the paraffin or the collodion method ( 450, 459 ) from 

 the jar of alcohol and plunge it into a vessel of water to remove the 

 alcohol. For staining put the slide of sections into a jar or shell 



