66 PRACTICAL HISTOLOGY. 



9. Picro-Lithium armine. This is even preferable to the fore- 

 going, because, in addition to staining nuclei red, it stains certain 

 other parts yellow. 



Lithium carmine . . . . . 50 cc. 



Saturated solution of picric acid . . . 100 ,, 



Mix the two slowly. If, after trying it, one or other colour is 

 too pronounced, add a little more of the other. 



The sections are to be treated with acid alcohol like the fore- 

 going. The acid alcohol, however, ultimately extracts the picric 

 acid. This is avoided by not leaving them too long in acid 

 alcohol. If the picric stain be removed, it may be restored at once 

 by dipping the section in absolute alcohol to which a little picric 

 acid has been added. 



10. Picro-Carmine. This most valuable reagent was introduced 

 by lianvier, and has the great advantage of giving a double stain 

 without the use of acid or alkali. 



(a.) Jtanvier's method of preparing it is as follows : To a 

 saturated watery solution of picric acid add a saturated ammoniacal 

 solution of carmine until precipitation just appears, i.e., until satura- 

 tion. The fluids must be well mixed. Leave it exposed in shallow 

 vessels to crystallise, but protect it from the dust. Crystals are 

 deposited, and also some amorphous carmine. After several weeks, 

 when its bulk is reduced to one-third, decant the liquid, filter, and 

 evaporate it to dryness on a water-bath. Redissolve it and the 

 crystalline deposit in water, filter, and evaporate to dryness. The 

 brown powder so obtained is dissolved in the proportion of i per 

 cent, in water. This fluid, prepared in this way, gives very satis- 

 factory results. 



(b.) Stdhr's Method. A very good solution is obtained by this 

 method. To 50 cc. water add 5 cc. liquor ammonise and i gram 

 carmine, which is rapidly dissolved. After complete solution, add 

 50 cc. of a saturated solution of picric acid. Set the mixture aside 

 for two or three days in a large open flat evaporating dish, and after 

 this time filter. To the filtrate add a drop of chloroform to prevent 

 the formation of fungi. 



Precautions. Preparations stained with picro-carmine are not 

 liable to be over-stained, and may be mounted in Fax-rant's solution 

 or glycerine acidulated with formic acid (i per cent.) [formic acid 

 sp. gr. 1. 1 6]. 



In staining sections with picro-carmine, cover the section with 

 picro-carmine, and after a few minutes remove the surplus pigment. 

 On no account should the section le jtlaced hi water. Water rapidly 

 extracts the picric acid and leaves the preparation stained with the 

 carmine only. Add a drop of Farrant's solution or formic glycerine, 



