Careful analysis of the situation has shown that a fat-soluble vitamine is present which can in the laboratory be separated from the fat.

This same vitamine is present in a variety of food materials--in whole milk, in egg yolks, in leaves of plants--but we have not studied it long enough to know just how much spinach we can substitute for a tablespoonful of butter so far as the vitamine is concerned.

We must await further investigations.

But we may rest assured that with a fairly liberal amount of milk and some green vegetables, possibly some beef fat, we need not fear any disastrous consequences from the substitution of some other fat for butter.

Where the diet is limited and the entire quantity of fat is not very large, it seems prudent to select oleomargarine made largely from beef oil and, where circumstances permit its use without the sacrifice of any other dietary essential, to use butter in the diet of growing children unless they get a full quart of milk apiece a day.
Changing our food customs is difficult because it means also changing our cooking customs.