228 PHYSIOLOGICAL CHEMISTRY. 



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

 differs from keratin in containing less sulphur. One of the chief 

 characteristics of collagen is, according to Hofmeister, the property 

 of being hydrolyzed by boiling acid or water with the formation 

 of gelatin. Emmett and Gies claim that under these conditions 

 there is an intramolecular rearrangement of collagen and the re- 

 sultant gelatin is consequently not the product of hydrolysis. The 

 liberation of ammonia from the collagen during the process ap- 

 parently 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 

 experiments is the tendo Achillis of the ox. According to Buerger 

 and Gies 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) 1.04 



Coagulable protein 0.22 



Mucoid i .28 



Elastin 1.63 



Collagen 3!-59 



Extractives, etc 0.90 



The mucoid mentioned above is called tendomucoid and is a gly- 

 coprotein. It possesses properties similar to those of other con- 

 nective tissue mucoids, c. g., osseomucoid and chondromucoid. 



Gelatin, the body which results from the hydrolysis of collagen 

 (see statement of Emmett and Gies above) is also an albuminoid. 

 It responds to nearly all the protein tests. It differs from the 

 keratins and collagen in being easily digested and absorbed. Gel- 

 atin is not a satisfactory substitute for the protein constituents of 

 a normal diet however, since a certain portion of its nitrogen is 

 not available for the uses of the organism. Gelatin from cartilage 

 differs from the gelatin from other sources in containing a lower 

 percentage of nitrogen. Tyrosine and tryptophane are not num- 

 bered among the decomposition products of gelatin, hence it does 

 not respond to Millon's reaction or the Hopkins-Cole reaction. 



EXPERIMENTS ON WHITE FIBROUS TISSUE. 



The tendo Achillis of the ox may be taken as a satisfactory type 

 of the white fibrous connective tissue. 



i. Preparation of Tendomucoid. Dissect away the fascia from 



