i;8 SCIENCE PROGRESS 



power of retaining gas, and as a consequence are quite unsuit- 

 able for bread-making. Dough made from rye-flour possesses 

 that power to only a limited extent, and accordingly occupies 

 an intermediate position as an article suitable for bread-making. 

 The difference between wheat and the other cereals in this gas- 

 retaining power is generally ascribed to the fact that wheat 

 contains gluten and the others do not, but Fleurent, as the 

 result of two series of analyses quoted by Bruyning, 1 gives 

 the percentages of gluten in rye, maize, and barley as higher 

 than that of wheat. The percentages of gluten are not the same 

 in various samples of the same cereal, and the one I am about 

 to quote is much lower than the average of flour made from 

 really strong wheats, but the table shows at a glance that the 

 essential difference between the cereals lies in the percentage 

 of gliadin which the gluten contains : 



The total gluten contains : 

 Gliadin, per cent., and Glutenin, per cent. 

 8-14 9283 



47'5° 5 2 '5° 



1431 8570 



1 5 '60 84*40 



i3"o8 86-92 



75'25 24-75 



The apparent contradiction between those who say, for 

 instance, that barley-flour contains no gluten and the analyses 

 of Fleurent which are here given, arises probably from a 

 difference in the methods of extraction. There is no necessity 

 to account with certainty for the apparent contradiction ; the 

 essential points for present purposes are that wheat and rye 

 are the only cereals used extensively for bread-making because 

 the others are quite unsuitable, that their suitability or unsuit- 

 ability depends upon their power to retain gas made in 

 fermentation, and that this depends upon the presence in the 

 flour of a substantial percentage of gliadin, a nitrogenous body 

 of a sticky nature which when wetted becomes figuratively the 

 cement in the concrete formed by the union of the two sister 

 nitrogenous bodies gliadin and glutenin. For several years it 

 ■was believed that the strength of flour depended on the ratio 

 of gliadin to glutenin in the gluten, but though the presence 

 of a large proportion of gliadin in the gluten is essential, the 

 idea that variations in the relative strengths of flours were 



1 La Valeur boidangire du Froment, p. 67. 



