BY DR. LAUDER BRUNTON. 445 



dryness on the water bath. Use the third for testing various 

 precipitants. 



Solubility. 1. Cold water. Dried gelatin will swell, but 

 will not dissolve. 2. Boil the water, it will dissolve. 3. Cold 

 dilute acids, and 4. Cold dilute alkalis, will dissolve it readily. 



Precipitation. It is precipitated by 1, tannic acid; 2, 

 mercuric chloride. Unlike albumin, pure gelatin is not pre- 

 cipitated by, 1, acetic acid and ferrocyanide of potassium ; 2, 

 many metallic salts, .as lead acetate, cupric or ferric sulphate. 

 It is not precipitated by acids or alkalis. 



Alteration by Boiling. Boil a solution of gelatin for some 

 time with an acid or alkali and let it cool. It will remain 

 fluid and will not form a jelly. Test its reactions. They will 

 be found the same as before. The same effect is produced by 

 prolonged boiling with water alone. 



48. Elastic Tissue. Elastin. The elastic fibres which 

 occur in the connective tissue in various parts of the body, 

 and are especially abundant in the middle coats of the aorta 

 and large arteries, and in the ligamentum nuclise, and ligamenta 

 subflava, are supposed to consist of elastin. 



Preparation. Remove the adhering cellular tissue from the 

 fresh ligamentum nuchse of an ox. Cut it into small pieces, 

 and boil it with alcohol and ether to remove the fat. J3oil it 

 for 24 hours with water, to dissolve the collagen, renewing the 

 water as it evaporates, or preventing evaporation (see 207). 

 Boil the residue with concentrated acetic acid for a consider- 

 able time ; remove the acetic acid by boiling with water, and 

 then boil with moderately dilute liquor sodae or potassre till it 

 begins to swell. Remove the alkali by boiling with dilute 

 acetic acid, then with water. Pivt the residue into cold hydro- 

 chloric acid ; let it remain for 24 hours, and then wash it with 

 water till the washings have no longer an acid reaction and 

 leave no residue on evaporation. 



Characters. The elastin which remains after the treatment 

 just described is yellowish and elastic while moist, but when 

 4ry becomes hard and brittle. 



Solubility. 1. Put a piece of dry elastin in water. It will 

 swell up but will not dissolve. 2. Boil the water. Unlike the 

 collagen of connective tissue, it will not dissolve. It does not 

 form gelatin, and the water will not gelatinize on cooling. 3. 

 It does not dissolve in alcohol, ether, or acetic acid, though it 

 swells in the latter. 4. Boil it with a strong solution of 

 caustic potash ; it will dissolve. 



Precipitation. Neutralize the solution in potash with hy- 

 drochloric or other acid. No precipitate will fall. Add tannin 

 to the neutral solution. A precipitate will be produced. No 

 other acids cause a precipitate. 



Reactions. 1. Xanthoprotein reaction. Put a piece of elas- 



