HISTOLOGICAL DEMONSTRATIONS. 125 



or three weeks, occasionally shaking or stirring the mixture, 

 then filter, and preserve in corked or stoppered bottles. 

 (Bedtc.) 



SKIN. 



223. Methods. a. Very good preparations may be 

 made of the skin hardened in the mixture of chromic 

 acid and spirit, as described in 16. The sections may 

 be advantageously stained with picro-carmine. They are 

 best mounted stained or unstained in Farrants' solution 

 or in glycerine. Stained sections may, however, also be 

 mounted in dammar. 



b. The method of digestion may be applied to the skin with 

 advantage (W. Stirling] for the purpose of studying the arrangements 

 of the muscular and elastic fibres. Mix iCC pure hydrochloric acid 

 with 5ooCC water, and add I gramme pepsine.* After keeping the 

 mixture at 38 C. for three hours, shake it thoroughly. Stretch a piece 

 of skin of man or dog, as fresh as possible, over the mouth of a glass 

 dialysing jar, and tie it firmly round the jar to keep it stretched. 

 Digest the skin in the above fluid at 38 C. for a period varying from 

 two to eight hours, according to the size and age of the skin. Young 

 skin digests more quickly than that which is old. It is advantageous 

 to use only about lOoCC of the digestive fluid at one time, and to 

 change the fluid every second hour if the piece of skin be large, in 

 order to remove the peptones, and thereby facilitate the digestive 

 process. After partial digestion, place the skin in water for twenty- 

 four hours. In this it becomes swollen and transparent. It can then 

 be hardened in the ordinary fluids, and stained with logwood or carmine. 

 By the above process the white fibrous tissue swells up and becomes 

 extremely transparent, thus permitting of a clear view of the other 

 tissues. 



c. The outlines of the cells of the rete mucosum may be well shown 

 by treatment with osmic acid, as described in 8jB. 



d. The epidermic cells may be rendered prone to separate by 

 maceration in potassium bichromate solution, as described in 870. 



e. Staining with gold and osmic acid is serviceable for the demon- 

 stration of the structure of the tactile corpuscles and their connection 

 with nerves. (See Thin, Journ. of Anat. and P/iys., vol. viii. 30.) 



224. Structure of the Skin. Examine the V. S. 

 human skin already prepared ( 87). 



(L.) In the epidermis observe the rete mucosum below, 



* 1\& pepsina porci of the British Pharmacopoeia may be conveniently 

 employed. 



