EPITHELIAL AND CONNECTIVE TISSUES 351 



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. 



(a) Solubility. Cut the collagen into very fine pieces and try its solubility 

 in water and dilute and concentrated acid and alkali. 



(b) Millon's Reaction. 



(c) Biuret Test. 



(d) Xanthoproteic Reaction. 



(e) Glyoxylic Acid Reaction (Hopkins-Cole). 



(f) Test for Unoxidized Sulphur. Take a large piece of collagen in a test- 

 tube and add about 5 c.c. of potassium hydroxide solution. Heat until the col- 

 lagen is partly decomposed, then add 1-2 drops of lead acetate and again heat to 

 boiling. 



(g) Formation of Gelatin from Collagen. Transfer the remainder of the 

 pieces of collagen to a casserole, fill the vessel about two-thirds full of water 

 and boil for several hours, adding water at Intervals as needed. By this means 

 the collagen is transformed and a body known as gelatin is produced (see page 

 350). 



3. Gelatin. On the gelatin formed from the transformation of collagen in 

 the above experiment (g), or on gelatin furnished by the instructor make the 

 following tests : 



(a) Solubility. Try the solubility in the ordinary solvents (see page 22) 

 and in hot water. 



(b) Millon's Reaction. 



(c) Glyoxylic Acid Reaction (Hopkins-Cole). Conduct this test according 

 to the modification given on page 106. 



(d) Test for Unoxidized Sulphur. 



Make the following tests upon a solution of gelatin in hot water : 



(a) Precipitation by Mineral Acids. Is it precipitated by strong mineral acids 

 such as concentrated hydrochloric acid? 



(b) Salting-out Experiment. Saturate a little of the solution with solid 

 ammonium sulphate. Is the gelatin precipitated? Repeat the experiment 

 with sodium chloride. What is the result? 



(c) Precipitation by Metallic Salts. Is it precipitated by metallic salts such 

 as copper sulphate, mercuric chloride, and lead acetate? 



(d) Coagulation Test. Does it coagulate upon boiling? 



(e) Precipitation by Alkaloidal Reagents. Is it precipitated by such reagents 

 as picric acid, tannic acid, and trichloracetic acid? 



(f) Biuret Test. Does it respond to the biuret test? 



(g) Precipitation by Alcohol. Fill a test-tube one-half full of 95 per cent 

 alcohol and pour in a small amount of concentrated gelatin solution. Do you 

 get a precipitate? How would you prepare pure gelatin from the tendo Achillis 

 of the ox? 



II. YELLOW ELASTIC TISSUE (ELASTIN) 



The ligamentum nuchce of the ox may be taken as a satisfactory type 

 of the yellow elastic connective tissue. The principal solid con- 

 stituent of this tissue is elastin, a member of the albuminoid group. 



