FATS AND THEIR ECONOMICAL USE IN THE HOME. 3 
formed in the fermentation of milk and cream by lactic acid and bac- 
teria and to the presence of small particles of the curd. Similarly, 
the by-products, such as butyric acid, which are formed by the action 
of undesirable bacteria, may be absorbed by the fat and give rise 
to the undesirable flavor of butter of poor quality or that which has 
deteriorated. Musty flavors are doubtless due to the presence of 
the products of metabolism of molds which may be present in the 
fats. In the case of some fats, like those of beef and mutton, or 
the fish oils, it has apparently been impossible to remove entirely the 
flavor-giving substances by the ordinary methods of refining. 
The exact nature of the compounds causing the rancid taste and 
odor of fats is not known. It is believed by some investigators that 
free and unsaturated fatty acids are first formed by the hydrolysis 
of the fats and that in the presence of light and air these fatty acids 
are oxidized to odoriferous compounds (aldehydes, ketones, etc.), 
the presence of which is thought to be identical with rancidity. 
Very little is known of the nature of the combinations formed when 
culinary fats and other food materials are mingled in doughs, batters, 
etc. It is not definitely known to what extent these are mechanical 
mixtures and to what extent the ingredients have undergone chemical 
and physical changes. It is probable that the texture, and conse- 
quently the thoroughness of digestion of the finished bread or cake, 
depend in some degree upon such factors, nnd more information on 
this subject is desirable in order that the culinary processes may be 
more completely understood and controlled. 
THE PLACE OF FATS IN THE DIET. 
The chief value of fats in nutrition is that they furnish energy 
which the body requires to perform its work. The ideal diet should 
contain sufficient quantities of fat and carbohydrates to insure it the 
required amount of energy, as well as a sufficient quantity of protein 
to supply the necessary nitrogen for growth and repair of the body, 
also mineral matter for growth and other body needs, and vitamins 
or similar bodies required to render the diet adequate for maintenance. 
Since fats furnish 2J times as much energy, pound for pound, as do 
proteins and carbohydrates (1 pound of fat furnishing about 4,000 
calories, and 1 pound of protein or carbohydrate only about 1,800 
calories) , and since they are both wholesome and palatable, they are 
very commonly used to increase the energy value of the diet. Fur- 
thermore, they are especially useful as a source of energy where an 
excess of carbohydrates in the diet is to be avoided, as in cases of 
diabetes or certain forms of indigestion. 
The consumption of some fat is apparently universal, although the 
amount eaten varies within rather wide limits. The diet in the 
polar regions represents one extreme, fat being used in quantity with 
