But what bearing has all this upon the dietetic use of nuts? The relation is very direct and very important. The situation developed as a result of the World War made very clear to everybody how close the world has arrived to the point where the careful economizing of our food resources will be absolutely necessary. The rapid increase of the world's population which has occurred, especially within the last two centuries, is a hew world experience. Two hundred years ago the average length of human life was less than 20 years, as it still is in Mexico and some other parts of the world where the life-saving influence of modern sanitation and health conservation have not had an opportunity to exercise their influence. In former times great epidemics devastated whole continents so frequently that the world's population barely held its own from century to century. In many instances whole tribes were wiped out. Such catastrophes are now almost unknown, although we still have with us the plagues of influenza, tuberculosis, syphilis, and pneumonia. Even these, however, are being conquered, so that their destructive influence is being stayed.
At the present rate at which the population of the world is increasing, the time is certainly not far distant when it will be necessary to utilize in the most economical manner possible every acre of soil capable of producing food. During the war the attention of agriculturists was very forcibly called to the enormous waste involved in our so-called animal industry. The first measure of food economy adopted in Germany at the beginning of the war was the slaughter of a large part of livestock. The same measure was adopted in Scandinavian countries and in all parts of central Europe. This was absolutely necessary, as Lusk and numerous other authorities have shown, for the reason that to produce one pound of water-free food in the form of beef or mutton requires the consumption more than 30 pounds of digestible food material. The cow is a much more economical means of food transformation, requiring the consumption of only a little more than 5 pounds of food for each pound produced, so that the waste of food in the production of milk is less than one-fifth as much as in the production of meat. This has led the food economists to recommend the reduced use of meat and the increased use of milk as a source of the complete protein required for sound nutrition. McCollum and other authorities, including representatives of the United States Department of Agriculture, have within the last four years persistently urged upon the public the importance of using more milk and less meat, and not simply as a matter of economy but as a matter of health as well, for it has been shown that the protein of milk is even superior to that of meat. It was found, indeed, that by the use of a few ounces of milk daily, a pint and a half, in connection with a dietary otherwise consisting wholly of foods derived from the vegetable kingdom, the body will be amply supplied with complete proteins, the milk not only furnishing protein of a superior character but serving also to supplement the proteins of the cereals, roots and other vegetable foods, supplying the amino-acids which they lack so as to render them also available for tissue growth and reconstruction.