HISTOLOGICAL METHODS. 171 



must not be made too transparent, e.g. unstained spleen, 

 alimentary canal, lung, liver. Generally speaking, clove oil 

 and turpentine are too powerful as clarifying agents for 

 tissues not stained with such dyes as carmine and logwood. 

 When glycerine is used, the tissue is preserved in it. 

 When clove oil or turpentine is employed, the tissue is 

 preserved in dammar or Canada balsam. 



METHODS OF STAINING THE TISSUES. 



317. In staining the tissues, there are two points to be 

 especially borne in mind. i. The staining fluid may affect 

 some parts of the tissue more than others, or it may stain 

 some parts, and others not at all ; e.g. the nucleus is more 

 deeply tinged with carmine or magenta than the surrounding 

 protoplasm, epithelial cement is deeply stained by silver 

 nitrate, nerve fibrils by gold chloride. 2. The staining 

 fluid may affect the tissue with tolerable uniformity, and 

 prove serviceable by merely rendering very transparent 

 colourless parts more evident. 



318. Carmine. The use of this valuable dye for 

 histological purposes was first recommended by Gerlach. 

 It tinges protoplasts, the axial cylinders of white nerve 

 fibres, but not the modified protoplasm of which cilia and 

 muscular fibre consist. It is useful to have two fluids. 



a. Weak carmine fluid, an exceedingly good carmine 

 fluid for general purposes, is a modification of that proposed 

 by Beale. Beale's fluid is thus prepared : 



Carmine . . .10 grains. 



Strong ammonia . . 30 minims. 



Glycerine ... 2 ounces. 



Rectified spirit . . \ ounce. 

 Place the carmine in a test tube, add the ammonia, 

 boil for a few seconds, let the solution stand for an hour 

 with the test tube open, add the water, filter, add the spirit 

 and the glycerine, and allow the mixture to stand exposed 

 to the air until the odour of ammonia is scarcely percep- 

 tible, then keep it in a stoppered bottle. This fluid is, 

 owing to its density, slow in its action, and, although it 



