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. why 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, unlike the ‘‘ volatile” oils, it does not evap- 
orate at ordinary temperatures. A little of this oil may be 
separated for examination by soaking “‘ whole 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 oxygen; 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. 
—— EEE 
