170 PRACTICAL HISTOLOGY. 



sam, dammar. 2. By partially or completely dissolving 

 certain elements of the tissues, so as to permit of others 

 being seen. Acetic acid, caustic potash or soda, are used for 

 this purpose. These partially or completely dissolve the 

 soft albuminous parts of most tissues. 



312. Glycerine and acetic acid may be used together as 

 recommended by Beale. (Glycerine i oz., glacial acetic 

 acid 5 drops.) 



313. Acetic acid. The acid most commonly employed 

 is the ordinary pyroligneous acid. It contains 28 per cent 

 of anhydrous acid (or 33*3 per cent of glacial acid). It is 

 important for ordinary purposes not to employ the acid in 

 too concentrated a form. Pyroligneous acid i part, water 

 2 parts, is the dilution most useful for ordinary purposes, 

 but so great a dilution as 4 or 5 drops to an ounce of 

 water is sometimes very serviceable, e.g. for showing the 

 nerve terminations in striped muscle ( 100, Kblliker] and 

 for slowly softening white fibrous tissue. 



314. Caustic potash is sometimes used for rendering 

 albuminous tissues transparent, and for softening connecting 

 substances. A 30 per cent solution of the caustic alkali 

 in distilled water is the most generally useful solution 

 (Moleschotf). Ewart and Thin (Journ. of Anatomy and Physi- 

 ology, vol. x. p. 223) have recently recommended a solution 

 of caustic potash in an equal weight of distilled water as a 

 means of preparing the fibres of the crystalline lens. 



315. Glycerine, acetic acid, 2^^ potash, being all miscible 

 with water, may be employed to clarify tissues from which 

 water has not been removed. Oil of cloves, or other essen- 

 tial oil, turpentine, creosote, carbolic acid, render most tissues 

 transparent. As these do not mix with water, it must be 

 previously removed by drying the tissue, or by immersion 

 in alcohol, and then allowing the alcohol to escape. 



316. Tissues hardened in chromic or picric acid, and 

 in potass, bichrom., are rendered somewhat opaque, and 

 must in general be clarified. This is usually done by 

 adding a, clove oil ; b, turpentine ; c, glycerine. These 

 fluids have different powers a is stronger than b, and b is 

 stronger than c. Glycerine is employed for tissues that 



