352 PHYSIOLOGICAL CHEMISTRY 



In common with the keratins and collagen, elastin is an insoluble body 

 and gives the protein color reactions. It differs from keratin prin- 

 cipally in the fact that it may be digested by enzymes and that it 

 contains a very small amount of sulphur. 



It has been demonstrated that elastin has the property of absorb- 

 ing pepsin from the gastric juice and thus protecting it so the enzyme 

 can function later in the intestine 1 (see Chapter on Gastric Digestion). 



Yellow elastic tissue also contains mucoid and collagen but these are 

 present in much smaller amount than in white fibrous tissue, as may be 

 seen from the following percentage composition of the fresh ligamentum 

 nuchce of the ox as determined by Vandegrift and Gies. 2 



Water 57-57% 



Solids 42 . 43 



Inorganic matter o. 47 



Organic matter . . '41 . 96 



Fatty substance (ether-soluble) 1.12 



Coagulable protein 0.62 



Mucoid 0.53 



Elastin 31.67 



Collagen 7 . 23 



Extractives, etc o . 80 



EXPERIMENTS ON ELASTIN 



1. Preparation of Elastin (Richards and Gies). 3 Cut the ligament into fine 

 strips, run it through a meat chopper and wash the finely divided material in cold, 

 running water for 24-48 hours. Add an excess of half-saturated lime water, 

 (see note at the bottom of page 350) and allow the hashed ligament to extract 

 for 48-72 hours. Decant the lime water, remove all traces of alkali by washing 

 in water and then boil in water with repeated renewals until only traces of protein 

 material can be detected in the wash water. Decant the fluid and boil the liga- 

 ment in 10 per cent acetic acid for a few hours. Treat the pieces with 5 per cent 

 hydrochloric acid at room temperature for a similar period, extract again in 

 hot acetic acid and in cold hydrochloric acid. Wash out traces of acid by means 

 of water and then thoroughly dehydrate by boiling alcohol and boiling ether 

 in turn. Dry in an air-bath and grind to a powder in a mortar. 



2. Solubility. Try the solubility of the finely divided elastin, prepared by 

 yourself or furnished by the instructor, in the ordinary solvents (see page 22). 

 How does its solubility compare with that of collagen? 



3. Millon's Reaction. 



4. Xanthoproteic Reaction. 



5. BiuretTest. 



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

 the modification given on page 106. 



7. Test for Unoxidized Sulphur. 



1 Abderhalden and Meyer: Zeit. physiol. Chem., 74, 67, 1911. 



2 Vandegrift and Gies: Am. Jour. Physiol., 5, 287, 1901. 

 8 Richards and Gies: Am. Jour. Physiol., 7, 93, 1902. 



