THE VOLATILE PAKT OF PLANTS. 93 



strong alcohol Liebig first designated as vegetable fibrin. 

 Kitthausen found this to be a mixture of two bodies, 

 which he distinguished as gluten-casein and gluten-fibrin. 

 The latter is extracted fr<im gluten by hot weak alcohol 

 and separates on partially removing the alcohol by eyap- 

 oration. 



The albuminoids of crude gluten dissolve In very dilute potash-solu- 

 tion (i to 1 parts potash to 1,000 parts of water), and the liquid, after 

 standing some days at rest, may be poured off from any residue of 

 starch, On adding acetic acid in slight excess, the purified albuminoids 

 are separated In the solid state. By extracting successively with weak, 

 with strong, and with absolute alcohol, the gluten-casein of Bitthaus^n 

 remains undissolved. 



On evaporating the alcoholic solution to one-half, there separates, on 

 ■cooling, a brownish-yellow mass. This, when treated with absolute 

 alcohol, leaves glitten^flbrin nearly pure. 



Vegetable fibrin is readily soluble in hot dilute alcohol, 

 but slightly so in cold dilute, and not at all in absolute al- 

 cohol. On prolonged heating with alcohol, it becomes in- 

 soluble in that liquid. It does not dissolve in water. It 

 has no fibrous structure like animal fibrin, but forms, 

 when dry, a tough, horn-like mass. In composition it 

 approaches washed muscle, but differs considerably from 

 blood-fibrin. 



Wheat contains or yields* but a small proportion of 

 fibrin and less appears to exist in hard than in the soft 

 wheats. Rye contains less than wheat. Barley, from 

 which no gluten can be got, yields to alcohol a small pro- 

 portion of fibrin. 



Maize fibrin, Zein. — The meal of Indian corn, unlike 

 that of wheat and rye, when made into a dough, forms 

 no gluten, but it yields to warm, weak alcohol some 

 7 per cent of fibrin quite similar to that from wheat, 

 though of somewhat different composition. 



* Weyl and Bischof believe that gluten does not pre-exist in wheat 

 and rye, just as fibrin does not exist in living blood, but is a result of 

 chemical change during the wetting and kneading of the flour to a 

 dough. According to them a strong solution of common salt extracts 

 from wheat flour vegetable globulin (see p. 97), and the residue, when 

 kneaded with water, forms no gluten. If, however, the salt solution of 



globulin, in contact with the flour, is largely diluted with water, the 

 our will yield gluten by kneading. 



