34 CEREALS 



has wheat flour mixed with it. The fact that wheat con- 

 tains in largest amount a nutrient with such remarkable 

 properties as gliadin, is the chief reason why this grain was 

 prized above all others in ancient times, and whj' it has 

 come to be valued more and more highly as civilization has 

 advanced. 



31. Fats. One other constituent shown in the chart re- 

 mains to be mentioned. This is the fat or fixed oil, called 

 "fixed" because, unhke the "volatile" oils, it does not evap- 

 orate at ordinary temperatures. A little of this oil msiy be 

 separated for examination b}^ soaking " Avhole wheat" flour, 

 bran, or corn meal in naphtha, and then pouring off the latter 

 into a shallow dish. The naphtha will evaporate, leaving be- 

 hind the oil which it had dissolved. 



In chemical composition the fats agree with the carbohy- 

 drates in consisting of carbon, hydrogen, and oxj-gen; the 

 difference being that there is always less than half as much 

 oxygen as hydrogen. Like the carbohydrates their use as 

 food is for yielding warmth and strength, and they may make 

 the body fatter; but as in these respects fats are more than 

 twice as effective as carbohydrates their importance In the 

 various grains is much greater than would appear from the 

 comparatively small amounts which are present. This fact 

 enables us to understand the great value of maize, for ex- 

 ample, in fattening animals. 



With foods rich in oil there is this drawback, however, 

 that after a limited time they are apt to spoil with keeping, 

 while starchy foods remain practically unchanged as long 

 as they are dry. Thus wheat, which contains less oil than 

 maize, keeps better, and its deficiency in this ingredient we 

 fully make up for by eating butter on our bread. 



