CHAPTER XVI. 

 THE SKIN AND ITS SECRETIONS. 



IN the structure of the skin of man and vertebrates many different 

 kinds of substances occur which have already been considered, such as 

 the constituents of the epidermal formation, the connective and fatty 

 tissues, the nerves, muscles, etc. Among these the different horn struc- 

 tures, the hair, nails, etc., whose chief constituent, keratin, has been 

 spoken of in another chapter (Chapter II), are of special interest. 



The cells of the horny structure show, in proportion to their age, a 

 different resistance to chemical reagents, especially fixed alkalies. The 

 younger the horn-cell the less resistance it has to the action of alkalies; 

 with advancing age the. resistance becomes greater, and the cell-mem- 

 branes of many horn-formations are nearly insoluble in caustic alkalies. 

 Keratin (or the keratins) occurs in the horn structure mixed with other 

 bodies, from which it is isolated with difficulty. These are detected by 

 microchemical investigations, and according to UNNA x three different 

 substances can be detected in the horn substance, designated by him A, 

 B and C keratin. 



The .d-keratin, which forms the envelope of the horn and hair cells arid the 

 outer layer of the hair, is the purest keratin. It is not dissolved by fuming nitric 

 acid at the ordinary temperature and does not give the xanthoproteic reaction, 

 and its keratin nature is doubtful. The 5-keratin, which occurs as the- contents 

 of the nail cells, gives the xanthoproteic reaction like the C-keratin occurring in 

 hair, but differs from the C-keratin by being soluble in fuming nitric acid. 



Besides these substances, which have been called keratins, the horn 

 structure also contains other proteins which are soluble in pepsin- 

 hydrochloric acid. Among these we find residue of nuclei and the 

 so-called trichohyalin in the hair, which is a substance of unknown 

 constitution and characterized by great insolubility. From these 

 statements it is evident that we are here dealing with a mixture of 

 different substances and for this reason it is unnecessary to give the 

 older elementary analyses of the various epidermoidal structures. 



The quantity of sulphur and of mineral bodies is of certain interest. 

 The sulphur and cystine content of these structures can be found on 



1 Monatsch. f. prakt. Dermat., 44. 



789 



