464 



FOOD. 



[CH. XXV11I. 



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, and 

 the forms of grain poor in gluten cannot be made into dough 

 (oats, rice, &c.). Gluten does not exist in the flour as such, but 

 is formed on the addition of water from the pre-existing globulins 

 in the flour. 



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. Proteid, except in potatoes, is pretty abundant, and espe- 

 cially so in the pulses (lentils, peas, &c.). The proteid in the 

 pulses is not gluten, but consists of vitellin and globulin-like 

 substances. 



In the mineral matters in vegetables, salts of potassium and 

 magnesium are, as a rule, more abundant than those of sodium 

 and calcium. 



Bread. 



Bread is made by cooking the dough of wheat flour mixed 

 with yeast, salt, and flavouring materials. A ferment in the flour 

 acts at the commencement of the process, when the temperature 

 is kept a little over that of the body, and forms dextrin and 



