EPITHELIAL AND CONNECTIVE TISSUES 349 



ferentiated from all other animal hair or wool by its high content of 

 cystine. Human hair may yield nearly 12 per cent of this ammo-acid. 1 



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 water, dilute and concentrated 

 acid and alkali. 



2. Millon's Reaction. 



3. Xanthoproteic Reaction. 



5. Glyoxylic Acid Reaction (Hopkins-Cole). 



6. Test for Unoxidized 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 per- 

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

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

 keratins, collagen is insoluble in the usual protein solvents. It differs 

 from keratin in containing less sulphur. One of the chief character- 

 istics of collagen is, according to Hofmeister, the property of being 

 hydrolyzed by boiling acid or water with the formation of gelatin. 

 Emmett and Gies 2 claim that under these conditions there is an intra- 

 molecular rearrangement of collagen and the resultant gelatin is conse- 

 quently not the product of hydrolysis. The liberation of ammonia from 

 the collagen during the process apparently confirms this view. Collagen 

 gives Millon's reaction as well as the xanthoproteic and biuret tests. 



The form of white fibrous tissue most satisfactory for general ex- 

 periments is the tendo Achillis of the ox. According to Buerger and 

 Gies 3 the fresh tissue has the following composition: 



Water 62.87% 



Solids 37.13 



Inorganic matter 0.47 



Organic matter. 36.66 



Fatty substance (ether-soluble) i .04 



Coagulable protein 0.22 



Mucoid . . . . .1 . 28 



Elastin i . 63 



Collagen 31-59 



Extractives, etc 0.90 



1 Buchtala: Zeit. physiol. Chem., 85, 246, 1913. 



8 Emmett and Gies: Jour. Biol. chem., 3, xxxiii (Proceedings), 1907. 



1 Buerger and Gies: Am. Jour. Physiol., 6, 219, 1901. 



