PRACTICAL HISTOLOGY FOR MEDICAL STUDENTS. 17 



SO that a section of any thickness can be obtained. The in- 

 strument is also adapted for freezing tissues. All fine sec- 

 tions must jioat over the knife's surface, therefore the knife 

 must be wetted. (See above.) The sections must always be 

 manipulated with sable or camel's-hair brushes. 



How to render Tissues Transparent. — A. By impregnating- 

 them with fluids which strongly refract light, e. g. glycerine, 

 turpentine, clove oil, Canada balsam, dammar. B. By par- 

 tially or completely dissolving certain elements of the tissues, 

 so as to permit of others being seen — acetic acid, caustic soda, 

 or potash. These partially or completely dissolve the soft 

 albuminous parts of most tissues. 1. Price's glycerine is that 

 Avhich is used. 2. Glycerine and glacial acetic acid may be 

 used together. G. 1 oz., acid 5 drops. (Beale.) 3. The acetic 

 acid commonly used is ordinary pyroligneous acid. 4. The 

 solution of soda is caustic soda 1 part, water 20 to 30 parts. 

 These four fluids all mix Avith Avater, hence they are 

 employed to clarify tissues from which water has not been 

 removed. 5. Turpentine, clove or other essential oil, 

 creosote, render most tissues transparent. They do not mix 

 with water ; therefore water must be previously removed by 

 drying the tissue or by immersion in alcohol. 



Tissues hardened in alcohol or chromic acid are rendered 

 opaque, and must in general be clarified. This is generally 

 done by adding, a, clove oil ; h, turpentine ; c, glycerine. 

 These fluids have different powers — a is stronger than h, and 

 h is stronger than c. Glycerine is employed for tissues that 

 must notbe made too transparent, e.^. spleen, alimentary canal, 

 lung, liver. When it is used, the tissue is preserved in it. 

 When clove or turpentine oil are employed, the tissue is pre- 

 served in Dammar or Canada balsam. 



How to diminish the Transparency of Tissues. — ^Place them 

 in alcohol, chromic acid, or stain them with the following 

 substances : 



Hoio to Stain Tissues. — Attend to these points. The staining 

 fluid may affect some parts of the tissue more than others, or 

 it may affect some parts and others not at all. In this way it 

 differentiates one part from another — e. g. the nucleus more 

 affected by carmine or magenta than the surrounding plasm. 

 The staining fluid may affect the tissue uniformly, and prove 

 serviceable by merely rendering very transparent colourless 

 parts more evident — e.g. elastic lamina of cornea stained by car- 

 mine. 1. Carmine, two fluids necessary, a. Strong ammoniacal 

 solution for hardened nerve tissue. (See preparation of nerve 

 tissue, fljw^ea.) Z>,Beale's carmine fluid. Carmine, 10 grains; 

 strong ammonia, 30 minims ; glycerine, 2 oz. ; distilled water, 



VOL. XII. NEW SER. B 



