CHAPTER XIV. 



EPITHELIAL AND CONNECTIVE TISSUES. 

 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 sim- 

 ilar 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. 



EXPERIMENTS ON EPITHELIAL TISSUE. 

 Keratin. 



Horn shavings or nail parings may be used in the experiments 

 which follow : 



1. Solubility. Test the solubility of keratin in the ordinary sol- 

 vents (see p. 23). 



2. Millon' s Reaction. 



3. Xanthoproteic Reaction. 



4. A damkieuicz's Reaction. 



5. Hopkins-Cole Reaction. 



6. Test for Loosely Combined Sulphur. 



CONNECTIVE TISSUE. 



I. WHITE FIBROUS TISSUE. 



The principal solid constituent of white fibrous connective tissue 

 is the albuminoid collagen. This body is also found in smaller 

 percentage in cartilage, bone and ligament, but the collagen from 

 the various sources is not identical in composition. In common with 



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