212 



PRACTICAL PHYSIOLOGY 



nutritive constituents of foods. The following table gives their general 

 average composition : 



Water, 



Proteid, 



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 : 



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



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 per cent, of starch, about 8 per cent, of 

 proteid, and about I per cent, of fat. The proteid 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 I. 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. Eemove 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. 



