33 2 PHYSIOLOGICAL CHEMISTRY 



The mucoid just mentioned is called tendomucoid 1 and is a glyco- 

 protein. It possesses properties similar to those of other connective- 

 tissue mucoids, e.g., osseomucoid and chondromucoid. 



Gelatin, the body which results from the hydrolysis of collagen 

 (see statement of Emmett and Gies p. 331), is sometimes classed as an 

 albuminoid (see Chapter V). It responds to nearly all the protein 

 tests. It differs from the keratins and collagen in being easily digested 

 and absorbed. Gelatin 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 gelatin from other sources in containing a lower 

 percentage of nitrogen. Tyrosine and tryptophane are not numbered 

 among the decomposition products of gelatin, hence it does not respond 

 to Millon's reaction or the glyoxylic acid reaction. Cystine is also 

 absent. 



EXPERIMENTS ON WHITE FIBROUS TISSUE 



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

 the white fibrous connective tissue. 



1. Preparation of Tendomucoid. Dissect away the fascia from about the 

 tendon and cut the clean tendon into small pieces. Wash the pieces in running 

 water, subjecting them to pressure in order to remove as much as possible of 

 the soluble protein and inorganic salts. This washing is very important. Trans- 

 fer the washed pieces of tendon to a flask and add 300 c.c. of half-saturated lime 

 water. 2 Shake the flask at intervals of twenty-four hours. Filter off the pieces 

 of tendon and precipitate the mucoid with dilute hydrochloric acid. Allow the 

 mucoid precipitate to settle, decant the supernatant fluid and filter the remainder. 

 Test the mucoid as follows : 



(a) Solubility. Try the solubility in water, sodium choride, dilute and con- 

 centrated acid and alkali. 



(b) Biuret Test. First dissolve the mucoid in potassium hydroxide solution 

 and then add a dilute solution of copper sulphate. 



(c) Test for Unoxidized Sulphur. 



(d) Hydrolysis of Tendomucoid. Place the remainder of the mucoid in a 

 small beaker, add about 30 c.c. of water and 2 c.c. of dilute hydrochloric acid 

 and boil until the solution becomes dark brown. Cool the solution, neutralize 

 it with concentrated potassium hydroxide, and test by Fehling's test. With a 

 reduction of Fehling's solution and a positive biuret test what do you conclude 

 regarding the nature of tendomucoid? 



2. Collagen. This substance is present in the tendon to the extent of 

 about 32 per cent. Therefore in making the following tests upon the pieces of 

 tendon from which the mucoid, soluble protein, and inorganic salts were removed 

 in the last experiment, we may consider the tests as being made upon collagen. 



1 Cutter and Gies: Am. Jour. Physiol., 6, 155, 1901. 



2 Made by mixing equal volumes of saturated lime water and water from the faucet. 



