244 MACERATION, DIGESTION, AND CORROSION. 



must be taken, and placed in 4 or 5 c.c. of weakly iodised serum in 

 a well-closed vessel. After one day's soaking the maceration is 

 generally sufficient, and the preparation may be completed by 

 teasing or pressing out, as indicated last ; if not, the soaking must 

 be continued, fresh iodine being added as often as the serum becomes 

 pale by the absorption of the iodine by the tissues. By taking this 

 precaution the maceration may be prolonged for several weeks. 



This method is intended to be applied to the preparation of fresh 

 tissues, the iodine playing the part of a fixing agent with regard to 

 protoplasm, which it slightly hardens. 



514. Iodide of Potassium (ARNOLD, Arch. mik. Anat., Hi, 1898, pp. 135 

 and 763). 10 c.c. of 10 per cent, aqueous sol. of potassic iodide with 5 

 to 10 drops of a similar solution, containing also 5 per cent, of iodine. 



515. Alcohol. RANVIER employs one-third alcohol (1 part of 

 90 per cent, alcohol to 2 parts of water). Epithelia will macerate 

 well in this in twenty-four hours. It macerates more rapidly than 

 iodised serum. 



Other strengths of alcohol may be used, either stronger (equal 

 parts of alcohol and water) or weaker (J alcohol, for isolation of the 

 nerve-fibres of the retina, for instance THIN). 



516. Salt Solution. Ten per cent, solution of sodium chloride is 

 a valuable macerating medium. Weaker strengths, down to 0-6 per 

 cent., are also used. 



517. MOLESCHOTT and Piso BORME'S Sodium Chloride and Alcohol 



(MOLESCHOTT'S V ntersuchungen zur Naturlehre, xi, pp. 99 107 ; 

 RANVIER, Traite, p. 242). Ten per cent, solution of sodium chloride, 

 5 volumes ; absolute alcohol, 1 volume. 



For vibratile epithelium RANVIER finds the mixture inferior to 

 one-third alcohol. 



518. Sodium Chloride and Formaldehyde. GAGE recommends the 

 addition of 2 parts of formalin to 1,000 parts of normal salt solution 

 (quoted from FISH, Proc. Amer. Mic. Soc., xvii, 1895, p. 328). 



519. Caustic Potash, Caustic Soda. These solutions should be 

 employed strong, 35 to 50 per cent. (MOLESCHOTT) ; so employed 

 they do not greatly alter the forms of cells, whilst weak solutions 

 destroy all the elements. (Weak solutions may, however, be 

 employed for dissociating the cells of epidermis, hairs, and nails.) 

 The strong solutions may be employed by simply treating the 

 tissues with them on the slide. To make permanent preparations, 

 the alkali should be neutralised by adding acetic acid, which forms 



