696 SCIENCE PROGRESS 



distinction of these and other vegetable proteins, fractional 

 precipitation by ammonium sulphate (introduced by Hofmeister) 

 and the application of Hausmann's method proved most 

 useful. 



3. The Alcohol-soluble Proteins. — The substances belonging 

 to this class, for which the general name gliadin is proposed, 

 and which possess no direct analogues amongst the animal 

 proteins, 1 are characterised by their unusual property of being 

 easily soluble in dilute alcohol, some even being soluble 

 in 96 per cent, alcohol. Ritthausen was the first to point out 

 that the seeds of wheat, rye, barley, maize, and oats contain 

 proteins which are insoluble in water and salt solution, but 

 readily soluble in alcohol. In wheat these substances, together 

 with the insoluble phyto-casein (glutenin), form the so-called 

 gluten, the adhesive glue-like material, which is of the greatest 

 importance in bread-making, by giving the necessary tenacity to 

 dough. The chemical characteristics of this class are the high 

 amount of glutaminic acid and the absence of glycine and 

 lysine in their cleavage products. Only three substances of 

 this class have so far been studied to any degree. They 

 are called wheat gliadin, zein (from maize), and hordein (from 

 barley). 



Wheat Gliadin. — Ritthausen originally distinguished three 

 alcohol-soluble substances in wheat which he called gliadin 

 (plant glue), glutenfibrin, and mucedin. He was, however, 

 unable to separate them quantitatively, and subsequent investi- 

 gators, especially Osborne and Campbell, returned to the old 

 view of Taddei's that there is only one alcohol-soluble substance, 

 for which they retained the name of gliadin. It seems, however, 

 preferable to call it wheat gliadin in distinction from the 

 group name. It is identical with the substance obtained from 

 rye, and amounts to 4 to 5 per cent, of the grain. It is 

 insoluble in absolute alcohol, but easily soluble in 70 to 80 

 per cent, alcohol, and is precipitated from these solutions by 

 the addition of water. It is especially characterised by the 

 high percentage of glutaminic acid, which it furnishes on 

 hydrolysis, amounting to 36 to 37 per cent, and the total 

 absence of lysine among its cleavage products. On account 

 of the strikingly different percentages of cleavage products 

 from those of animal proteins, it was chosen by Abderhalden 

 1 Pick suggests a similarity to the proto-albumoses. 



