INTRODUCTION. xlv 



(i) Iodine Green. A saturated watery solution may be made and diluted as it is required, 

 or a one per cent, solution may be prepared. It stains rapidly, and the stain cannot be 

 removed by washing. It is one of the most useful of the aniline dyes, especially for double- 

 staining (p. xlvi). It stains mucous glands green, and acts similarly on unossified cartilage- 

 Preparations stained with it must be mounted in dammar. Do not leave the stained sections 

 long in spirit, which partially removes the dye. 



(/) Rosein is soluble in spirit, and so is useful for double-staining when the sections are to 

 be mounted in dammar. See retina. Ordinary methylated spirit does quite well as a solvent 



Many other aniline dyes are employed, but the above are certainly the most useful. 



(g) Eosin, though not an aniline dye, may for convenience be taken here. It yields a 

 rose-coloured dichroic fluid, when dissolved. Dissolve i part in 1,500 of water. Tissues 

 become stained in a few seconds. After staining, place them in water slightly acidulated with 

 acetic acid (one per cent.), to remove the excess of pigment and to ' fix ' the remainder. 

 Sections may be examined either in glycerine or in dammar. For some purposes, as for 

 staining the haemoglobin of coloured blood-corpuscles, it is used as an alcoholic solution. It 

 is very useful in the study of developing coloured blood-corpuscles. 



METALLIC SOLUTIONS. 



(a) Silver Nitrate. Dissolve i grm. of silver nitrate in 100 c.c. of distilled water. For use 

 dilute this to or ^ per cent, solution. Wash the tissue to be stained (which must be quite 

 freslf) in distilled water to remove chlorides, place it in the silver solution for five minutes, or 

 until it becomes of a whitish appearance, then remove it, wash it in ordinary water, and 

 expose it in water, or alcohol and water, to diffuse daylight till it becomes brown in colour. 



Silver nitrate solution is used where it is desired to bring into view the existence of epithelial 

 cells e.g. on serous membrane, lining arteries, lymphatics, capillaries, or the air-cells of the 

 lung. It acts upon the intercellular substance, or cement, and when the tissue is exposed to 

 the action of light, it is precipitated in the intercellular substance as the black oxide, in fine 

 black lines, and thus the cells are mapped one from another. These lines are known as 

 ' silver lines.' It also stains the intercellular substance of cartilage and the cornea. The prepara- 

 tions may be preserved in glycerine or dammar, and ought to be kept in a dark place, as they 

 are apt to spoil when long exposed to light. 



(U] Gold Chloride. Solutions from \ per cent, to 2 per cent, are employed. 



1. Place the perfectly fresh tissue in the gold solution (^ per cent.) for twenty to thirty 

 minutes, wash it in water, and then expose to daylight in water slightly acidulated with 

 acetic acid (2 or 3 drops of acetic acid to i oz. of water) until it becomes of a purplish colour. 



2. Or the following method may be employed, especially where the tissue is dense and it is 

 not desirable to retain the epithelium. Cut a fresh lemon in two, squeeze out the juice and fil- 

 ter it through muslin. Place the perfectly fresh tissue e.g. cornea in the juice for five or seven 

 minutes, wash it in water to remove the juice,,and steep it in a one per cent, solution of gold for 

 twenty minutes, or half an hour. Wash off the surplus gold, and place the object in a mixture 

 of one part of formic acid to four of water. Put the bottle in a dark place. After twenty- 

 four hours the gold is completely reduced. All the. epithelium, however, is removed by the 

 formic acid. This method is the best for demonstrating the terminations of nerves in muscle. 



Gold is especially useful for staining nerve-fibrils e.g. in the cornea -and also for connec- 

 tive tissue-corpuscles. 



Under each tissue where gold is useful, special directions are given for its employment. 



