72 PRACTICAL HISTOLOGY. 



hardened in watery solutions of chromic acid it is otherwise. It is 

 sometimes very difficult to get them to stain. This may sometimes 

 be effected by soaking the sections previously in a dilute solution of 

 sodic carbonate. 



They are also very valuable in double and treble staining. 



In the case of preparations stained by haematoxylin or logwood, 

 over-staining may be got rid of by placing the sections in dilute 

 acetic acid. This will rapidly extract the surplus stain, but at the 

 same time, if allowed to act too long, it will make the remaining 

 part red. Great care should be taken afterwards by thorough 

 washing of the sections in water to remove every trace of the acid. 



C. Eosin. 



1. Eosin. This substance is readily soluble in alcohol and water. 

 Make a 5 per cent, watery solution. It gives a beautiful diffuse 

 rosy hue, and stains very quickly, in a minute or two. The 

 stronger solution can be diluted as required. It forms one of the 

 best ground-stains in contrast to logwood or one of the numerous 

 aniline dyes. When using it as a double stain, e.r/., logwood and 

 eosin, stain the section first of all in logwood, and if it is to be 

 mounted in balsam, clarify with clove-oil in which a little eosin has 

 been dissolved. Sections stained with it can be mounted in balsam, 

 Farrant's solution, or glycerine. It is a specific stain for the 

 haemoglobin of red blood-corpuscles, as it stains it, even after 

 hardening in chromic salts, a copper-red colour, while it also stains 

 the granules of certain leucocytes of the blood of a reddish tint. It 

 is used very extensively, and in a very dilute solution is a good 

 stain for cartilage and striped muscle. 



D. The Aniline Dyes. 



Watery or alcoholic solutions of the aniline dyes stain sections 

 with great rapidity. The word "stain" is perhaps not quite the right 

 word to use. It is rather a process of imbibition than staining 

 proper. One of the difficulties in using aniline dyes is the rapidity 

 with which sections have to be transferred from one liquid to another. 

 They are not used for staining in bulk. After staining and dehydrat- 

 ing, it is best to clarify the sections (except in special cases) with 

 cedar or bergamot oil or xylol. The sections are mounted in balsam, 

 not in glycerine, as the latter dissolves the dyes. 



They are amongst the most valuable so-called staining reagents 

 we possess, and although many of them do riot yield permanent 

 preparations the colour fading after a time still the results 

 obtained by their use are so important that it behoves the student 

 to use them frequently. It is most important that they should be 

 obtained from reliable sources. 



