86. Milk Fat

Milk fat contains not only the three principal fats, but also the others mentioned, butyrin, cap-roin, caprylin, caprin, laurin, and myristin,in small proportions, and these latter tend to give butter certain properties that distinguish it from the other animal fats, which are almost wholly palmatin, olein, and stearin. These special butter fats are liquid at ordinary temperatures. Doubtless the flavor, texture, and resistance of butter to the effects of heatare muchinfluenced by the proportionsof the numerous fats it contains, but there is much connected with this subject of which we are still ignorant.

87. Fatty Acids

Free, fatty acids exist in nature. They are not found in butter, lard, and tallow unless these substances have undergone fermentations, or, as we say, have become rancid. The characteristic flavor of strong butter is due to free butyric acid, which, because of fermentations, has parted from the glycerin with which it was originally combined in the milk. In plant oils, on the other hand, are found considerable proportions of the free fatty acids, some of which have not been discovered so far in animal fats, either free or uncombined.

88. Ether-Extracts

Perhaps no one has studied plant oils more thoroughly than Stellwaag, who investigated the ingredients of the ether- and benzine-extracts from plants. His results show that not only do these extracts include substances which are not fats, but that a considerable proportion of free, fatty acids is always present, sometimes in quantities exceeding the neutral fats: -

Table XVIII. Composition of Ether-Extracts (Per Cent)

It appears, as before stated, that ether-extract, especially that from vegetables, may consist, to some extent, of materials which should not be classed among the fats. The extracts from the grains proved to be nearly all oil. Moreover, the grain oils were made up principally of glycerides, and those from potatoes and beets consisted largely of free, fatty acids.

89. Lecithins

There is a group of bodies closely related to the fats, which are oft,en called the phosphorized fats. Reference is made to the lecithins. It has previously been stated that neutral fats are combinations of fatty acids and glycerin (glycerol). Lecithins are compounds in which one of the radicals of a fatty acid is replaced by a compound of phosphoric acid. They are widely distributed in nature. They appear to be an active component of every cell, both of vegetable and animal tissue, and they are especially abundant in seeds, in the nerve system, in fish, eggs, and in the yolk of eggs. These bodies evidently fill an important place in plant and animal nutrition. These are good theoretical reasons for suggesting that lecithins serve as a stepping stone to the synthesis of the nucleoproteins. In digestion they behave like the true fats.