REACTIONS CHARACTERISTIC OF INDIVIDUAL PROTEIDS 97 



3. Albumins, a. Solubility in water and in neutral salts. Test 

 each statement. Albumin is soluble in distilled water, dialyze out the traces 

 of salts. It is soluble in saturated sodium chloride and saturated magnesium 

 sulphate. It is insoluble in saturated ammonium sulphate. 



b. Heat coagulation. Mount a test tube containing 5 c.c. faintly acid 

 egg-albumin in a 500 c.c. beaker of water which is supported by a gauze and 

 ring stand. Suspend a thermometer bulb in the middle of the albumin 

 solution. Gradually heat the beaker of water, stirring constantly, thus uni- 

 formly heating the albumin. Coagulation takes place at from 73 to 75 C., 

 but turbidity a little earlier. 



4. Globulins, a. Solubility in water and in neutral salts. Test 

 the following statements, using serum globulin. Globulin is insoluble in 

 distilled water. It is soluble in dilute neutral salt solutions sodium chlo- 

 ride, magnesium sulphate, ammonium sulphate. Globulin is precipitated 

 by adding sodium chloride or magnesium sulphate to complete saturation. 

 Fibrinogen is precipitated by half -saturated magnesium sulphate. Globulins 

 are precipitated by adding to their solution an equal volume of saturated 

 ammonium sulphate, i.e., by half -saturated solution. 



b. Heat coagulation. Test the temperature at which globulins are heat 

 coagulated by the method described above, on a sample of salted plasma 

 for nbrinogen which coagulates at 56 C., and on serum globulin which 

 coagulates at 73 C. 



5. Albuminates. Digest egg albumin in 0.2 per cent hydrochloric 

 acid for an hour and test: 



a. Solubility. It is insoluble in neutral solutions and in saturated neu- 

 tral salts, but soluble in dilute acids and alkalies. 



b. Heat coagulation. It is not coagulated by heat. 



6. Albumoses and Peptones. These proteids are formed in 

 the alimentary canal in the process of digestion under the influence of the 

 enzymes, pepsin and trypsin. Make a 5 per cent solution of Armour's pep- 

 tone (which contains chiefly albumoses) and test: 



a. Heat coagulation. These proteids are not coagulated. 



b. Alcohol. When added to excess, a precipitate occurs, but when 

 collected on a filter the precipitate may be redissolved in water. 



c. General proteid reactions. These proteids fail to give many of the 

 precipitations, but give the color changes. The biuret test yields a rose 

 pink color. 



d. Neutral salts. Albumoses are insoluble in saturated ammonium 

 sulphate. Filter and test the filtrate for proteid. It gives the biuret test. 

 This is due to peptones which are soluble in all salt solutions. 



7. Ferment and Heat-Coagulated Proteids. Boiled egg white 

 should be used for the example of the former, and fibrin for the latter. Test 

 for the color reactions, experiment i, which they both give. These pro- 



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