364 



PRACTICAL PHYSIOLOGY 



cultivated grasses, and they all contain representatives of the various 

 nutritive constituents of foods. The following table gives their general 

 average composition : 



Water, 



Protein, 



Carbohydrate, 



Fat, 



Mineral matter, 



10- 12 per cent. 

 10-12 per cent. 

 65-75 per cent. 

 0-5-8 per cent, 

 about 2 per cent. 



The more important varieties have the following composition : 



The most important of the cereal foods is wheat, of which it is 

 estimated that 6 bushels per head of population are consumed every 

 year. It is in the form of flour and bread that wheat is mainly 

 consumed. 



FLOUR. 



Ordinary white flour is obtained from the endosperm of wheat grains 

 and contains from 70 to 75 % of starch, about 8 % of protein, and about 

 1 % of fat. The protein is mainly of the nature of a globulin, and it 

 has the property of becoming viscid when mixed with water. This 

 viscid body is called gluten, and it is in virtue of this body that dough 

 is formed when water is added to flour, as in the manufacture of bread. 



EXPERIMENT III. Eoll up some flour loosely in a piece of muslin ; 

 place the bag thus formed in a small beaker containing some water and 

 knead it. The starch grains pass through the muslin into the water, 

 so that this soon becomes opaque and a sample placed in a test tube 

 gives a blue colour with iodine. Apply Trommer's test to another 

 sample and note that no sugar is present. After kneading for some 

 time remove the bag and examine the contents, when it will be found 

 that a sticky mass has been produced gluten. Remove a piece of this 

 and suspend it in water in a test tube. Apply Millon's and the 

 xanthoproteic tests to it, and note that the suspended pieces of gluten 

 react positively to both tests. 



1 Taken from Hutchison's Food and the Principles of Dietetics. 



