PROTEINS 277 



flour add in small portions enough water to make a dough. 

 Knead this thoroughly in running water until it is washed free 

 of starch. Press out as much water as possible from the solid 

 residue, which is known as gluten. Add 250 c.c. of 70% alcohol 

 (prepare this by diluting 185 c.c. desk alcohol, 95%, to 250 c.c.) 

 and knead up thoroughly with the hand. Shake often, and allow 

 to stand until the next laboratory period, or extract for an hour 

 on the water bath. Filter off the gliadin solution from the residue 

 which is mainly glutenin. Evaporate the gliadin solution on the 

 water bath. On the residue make the following tests. Test its 

 solubility in water and 10% NaCl. Try the Millon and xantho- 

 proteic tests. 



24. Glutelins. The only member of this group which has 

 been carefully studied is the glutenin of wheat. It may be pre- 

 pared from wheat flour by allowing 0.2% KOH to act on the 

 insoluble residue left after the gliadin has been completely ex- 

 tracted. This alkaline extract is then neutralized with HC1, 

 when the glutenin precipitates. 



Albuminoids. These proteins are distinguished by their 

 insolubility in neutral solvents. They form the principal or- 

 ganic components of the supporting framework of the body and 

 of hair, nails, horn, etc. 



Keratin. 25. Test the solubility of horn in water and 10% 

 NaCl. 



26. Place a few pieces of horn in a few cubic centimeters each 

 of artificial gastric and pancreatic juice, add a small amount of 

 toluol, and set in the incubator until the next period. Horn is 

 not digested by gastric or pancreatic juice. Conclusions as to 

 the digestibility of horn are drawn from the appearance of the 

 pieces. It is not possible to use the color tests for ascertaining 

 whether or not horn has been digested, as the pancreatic and 

 gastric ferment preparations themselves contain soluble proteins 

 in amounts sufficient to give positive color reactions. 



27. Suspend small pieces of horn in water and try the Millon 

 and xanthoproteic tests. Test for loosely combined sulphur. All 

 of these tests should be positive. 



