58 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



grain. 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 addi- 

 tion ; 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 soluble proteins (e.g. globulins) 

 in the flour. It is a mixture of several proteins (gliadin, mucedin, 

 gluten-fibrin, &c.). 



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. 



Protein, except in potatoes, is pretty abundant, and especially so 

 in the pulses (lentils, peas, &c.). The protein 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 sugar from the 



