CHAPTER XIX 



EPITHELIAL AND CONNECTIVE TISSUES 

 TEETH 



Epithelial Tissue (Keratin). The albuminoid keratin constitutes 

 the major portion of hair, horn, hoof, feathers, nails, and the epidermal 

 layer of the skin. There is a group of keratins the members of which 

 possess very similar properties. The keratins as a group are insoluble 

 in the usual protein solvents and are not acted upon by the gastric 

 or pancreatic juices. They all respond to the xanthoproteic and Millon 

 reactions and are characterized by containing large amounts of sulphur. 

 Keratin from any of its sources may be prepared in a pure form by 

 treatment, in sequence, with artificial gastric juice, artificial pancreatic 

 juice, boiling alcohol, and boiling ether, from twenty-four to forty- 

 eight hours being devoted to each process. 



The percentage composition of some typical keratins is given in the 

 following table: 



The composition of human hair is influenced by its color and by the 

 race, sex, age and purity of breeding of the individual. 3 It may be dif- 



1 Mulder: Versuch einer allgem. physiol. Chem., Braunschweig, 1844-51. 

 *Horbaczewski: Ladenburg's Hand-worterbuch d. Chem., 3. 

 Rutherford and Hawk: Jour. Biol. Chem., 3, 459, 1907. 



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