488 FOOD [CH. XXX. 



protein entirely in the form of meat, it would be necessary for him 

 to consume about 500 grammes (i.e. a little more than 1 Ib.) of meat. 



Flour. 



The best wheat flour is made from the interior of wheat grains, 

 and contains the greater proportion of the starch of the grain and 

 most of the protein. Whole flour is made from the whole grain 

 minus the husk, and thus contains not only the white interior but 

 also the harder and browner outer portion of the grain and the 

 germ or embryo plant. This region contains a somewhat larger pro- 

 portion of protein. Whole flour contains 1 to 2 per cent, more 

 protein than the best white flour, but it has the disadvantage of 

 being less readily digested. Brown flour contains a certain amount 

 of bran in addition ; it is still less digestible, but is useful as a mild 

 laxative, the insoluble cellulose mechanically irritating the intestinal 

 canal as it passes along. 



The best flour contains very little sugar. The presence of sugar 

 indicates that germination has commenced in the grains. In the 

 manufacture of malt from barley this is purposely allowed to go on. 



When mixed with water, wheat flour forms a sticky, adhesive mass 

 called dough. This is due to the formation of gluten. Gluten is a 

 mixture of two proteins namely, gliadin, which is soluble in alcohol, 

 and glutenin, which is soluble in alkali (see p. 433). The adhesive 

 character of gluten is due to gliadin ; grains which are poor in gliadin 

 (e.g. rice) cannot be used for bread-making. 



The following table contrasts the composition of some of the more 

 important vegetable foods : 



We see from this table 



1. The great quantity of starch always present. 



2. The small quantity of fat ; that bread is generally eaten with 

 butter is a popular recognition of this fact. 



3. Protein, except in potatoes, is pretty abundant, and especially 

 so in the pulses (lentils, peas, etc.). The protein in the pulses is not 

 gluten, but consists mainly of globulins. 



In the mineral matters in vegetables, salts of potassium and mag- 

 nesium are, as a rule, more abundant than those of sodium and calcium. 



