abundant meat supply is to be maintained, it must be in some other way. With such a density of population as we may reasonably expect, it will no longer be a question of producing bread or meat, but of producing bread and meat. All the edible products which the farmers' acres can yield will be needed for human consumption and the function of the stock feeder in a permanent system of agriculture will be to utilize those inedible products in which so large a share of the solar energy is held and to render at least a portion of the latter available for human use. Meat and other animal products will be produced, not as luxuries for the tables of the rich, but as a means of conserving energy for human use, both directly through the food thus rescued from waste and indirectly by setting free edible plant products for man's use. The stock feeding of the future will be a very different matter from the simple grazing of cattle in summer or the lavish feeding of corn in winter. It will be a highly artificial process, dealing with feeding stuffs unfamiliar to the fathers and seeking to utilize to the utmost the energy of every available by-product. It will call for a degree and a kind of knowledge and skill far exceeding that which has sufficed in the past.
Until within a comparatively few years, but little direct study has been devoted to these fundamental considerations, especially in the United States. While institutions for agricultural research have flourished, they have either concerned themselves with the more obvious problem of increasing crop production or else, in response to the demands of stockmen, have devoted their energies largely to seeking more efficient ways of converting corn into meat. In this latter respect, they have aided in exploiting rather than in conserving food resources, and it has been difficult to secure public interest or public funds for fundamental investigation looking toward the conservation of the food supply of the future.
More than a purely scientific interest, therefore, attaches to studies of the principles governing the utilization of the stored-up energy of feeding stuffs, particularly of by-product feeds, such as have been made during the past ten or twelve years by German investigators, particularly by Kellner at the Moeckern Experiment Station, and as are now being prosecuted by the Institute of Animal Nutrition of the Pennsylvania State College in cooperation with the Bureau of Animal Industry of the United States Department of Agriculture.
Such a study is far from being a simple matter. Essentially, of course, its method must consist in feeding the products under investigation to animals and ascertaining what proportion of their energy can be thus saved. The difficulty lies in the determination of the latter point. This must be accomplished with an accuracy and a degree of detail unattainable in the ordinary feeding experiment if the conclu-
