# Popular Science Monthly/Volume 79/November 1911/The Conservation of the Food Supply

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* THE CONSERVATION OF THE FOOD SUPPLY
By Dr. HENRY PRENTISS ARMSBY
INSTITUTE OF ANIMAL NUTRITION OF THE PENNSYLVANIA STATE COLLEGE
THE maintenance of the food supply is the basal problem of civilization. Before commerce or manufactures or mining can be carried on—before science or art or religion can flourish—man must be fed.
Hitherto, the people of the United States, thinly scattered over a country of vast extent and seemingly exhaustless fertility, have scarcely realized that there is such a thing as a food problem, but more and more frequently of late there are heard warnings of the danger of an inadequate food supply for our future millions and of the resultant peril to our democracy through the fostering of caste and class distinctions. That the problem is a serious one, even if it be not so immediately imminent as some would have us believe, admits of no reasonable doubt.
Now the problem of food supply is in essence a problem of energy supply. Food yields the energy which operates the bodily mechanism and upon the regularity and sufficiency of this energy supply depends absolutely all human endeavor. To produce those carriers of energy which we call foods is the chief function of the farmer. By means of the green leaves of his crops he entraps the energy of the sunlight and stores it up in the starches, fats and proteins of his wheat, corn, etc., to be liberated again in the body when these are used as food. The farmer as a food producer is the first link in the chain of human activities—the agent by whose labors the boundless stream of solar radiation is utilized for man's service—and the density of population which a country can support from its own resources is practically limited by the amount of solar energy which the farmer can recover in food products.
Clearly then in preparing to meet the future food problem the primary thing is to see to it that the farmer is taught how by means of tillage, fertilization, seed selection, crop rotation, and all the arts of good farming to accumulate as much as possible of the solar energy in his yearly crops. The proposition is sufficiently obvious and already commands popular support.
There is, however, another less evident aspect of the question. In order to feed the teeming millions of the future, it will not only be necessary to fix as much of the solar radiation as possible in the form of crops, but also to utilize the energy which the latter contain with the maximum of efficiency. When our population reaches half a billion, there will be little margin for waste.
​Now in view of our absolute dependence on solar radiation, it is a rather startling fact that but the smaller part of the energy stored up in the farmer's crops is directly available for man's use. Of that of the wheat crop, for example, fully sixty per cent, is contained in the straw and another 10 per cent, is rejected in the process of milling as bran and other by-products. In other words, only about 30 per cent, of the energy stored in an acre of wheat is directly available for human nutrition. Much the same thing is true of most other food crops, while the grasses and clovers, so important in all systems of agriculture, are, of course, entirely unavailable as food for man. Hitherto, our enormous surplus of food products has served to obscure the significance of this fundamental fact. Not only have we been able to export vast quantities of breadstuffs to less fortunate lands, but we have used other millions of bushels of edible products, especially corn, as food for domestic animals. America has been a country of cheap animal food—meat, eggs, milk, butter, cheese, etc.—and we have been fond of drawing the comparison between the abundant meat supply of our working classes and its comparative scarcity in the diet of the European laborer and, rightly or wrongly, have attributed much of the greater industrial efficiency of our workmen to this difference in diet.
But we are rapidly approaching an economic limit to the production of meat from edible grains. Such a conversion is an exceedingly wasteful process. Of the solar energy stored up in a bushel of corn, less than 3 per cent, is recovered in the edible portion of the carcass of the steer to which it is fed, while even in pork production this percentage scarcely rises to more than 16, and in milk production to about 18, and similar losses are observed in all branches of animal production. In other words, the stockman who feeds his animals on grain is expending energy available for human use as fuel for his animal machines for the sake of recovering a small fraction of it in higher priced and more palatable products, a process which can hardly fail to remind one of the reputed origin of roast pig. So long as our food supply was vastly in excess of our needs, such practises were doubtless economically justifiable. To the solitary hunter in the primeval forest it was a matter of comparative indifference whether he made his camp fire of underbrush or of the best grade of timber, but with lumber at its present price, the mill owner can afford only sawdust and refuse to feed his fires. In the past, speaking broadly, our meat production has consisted to a large extent in the exploitation of our food resources. There has been a choice between producing bread or meat, and the improvements in stock husbandry have been largely in the direction of more profitable exploitation. In the near future, we shall have to reverse this attitude and study the conservation of the food supply. Not much longer can we continue to take the children's bread and cast it to the brutes. If our ​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 ​conclusions are to pass beyond the empirical stage and lead to the establishment of general principles. For this purpose Kellner has used a form of the so-called Pettenkofer respiration apparatus, first devised many years ago by Professor v. Pettenkofer in Munich, while the Pennsylvania institution employs an instrument known as the respiration calorimeter, first devised by the late Professor W. O. Atwater for investigations in human nutrition and which has been enlarged and modified to adapt it for experiments upon domestic animals.
The central feature of both apparatuses consists of an air-tight chamber through which a measured current of pure air passes and within which the animal stands in a comfortable stall, where it can be fed and watered at will. The total energy contained in the feed of the animal is ascertained by determining the amount of heat which a sample of it produces when completely burned, while the energy escaping in the visible excreta is measured in the same way. Furthermore, by analyzing samples of the air-current before and after its passage through the chamber containing the animal the gaseous waste products given off by the latter are determined.
Finally, energy escapes from the animal in the form of heat. In the German experiments the amount of heat produced by the animal is virtually computed from the amount and kind of materials oxidized in the body. This may also be done in the experiments with the respiration calorimeter, but in addition this apparatus is provided with appliances for the direct determination of the heat given off, it being taken up by a current of cold water circulating through copper pipes and its amount measured with the aid of sensitive thermometers. In this way the total income and outgo of the animal can be compared, the difference showing how much of the energy of the food has been stored up as meat or fat, while a comparison of the observed with the computed heat production serves as a check on the accuracy of the experiments.
The method is not unlike that employed in locomotive testing plants like, e. g., that of the Pennsylvania Railroad at Altoona. Just as in the latter, the heat value of the fuel is measured, so in the experiments upon the animal the heat value of the feed, which is the fuel of the animal body, is determined. The losses in the visible excreta of the animal may be compared to unburned coal dropping through the grate, while the gaseous excreta correspond to the flue gases. A large amount of heat is given off in both cases, and the final balance of income and outgo makes it possible to trace exactly the use which the locomotive or the animal makes of the energy supplied to it.
The material or ration to be tested is fed for some three or four weeks with the greatest regularity. During the latter portion of this time, after the effect of the ration has become fully established, the animal spends from two to five days in the respiration apparatus or the
​calorimeter under the constant observation night and day of three or four skilled men. Its intake of food and energy, the losses in the excreta, the volume, composition and temperature of the air passing through the apparatus and in the case of the respiration calorimeter especially the temperature of the water used to take up the heat produced are matters of continuous record. A single "run" with the latter apparatus involves the recording of nearly 7,000 observations, while fully 25 samples of various sorts are taken whose subsequent analysis in the chemical laboratories involves the making of some 150 determinations.
From the results of these hundreds of weighings, records and analyses there is finally worked out a complete balance of income and outgo. Comparisons of these balances on different amounts and kinds of feed, with different animals, and under varying conditions, permit exact conclusions to be drawn regarding the nutritive effects of the rations consumed.
The investigations in progress relate to three different aspects of the general problem: First, how do different feeding stuffs compare with each other as to their content of energy and the proportion of it which is available to the animal? Second, what is the relative efficiency of different types of animals as converters of waste energy into human food? Third, how do the various conditions under which animals may be kept affect their efficiency in this respect? To the extent to which it becomes possible to answer these questions for the different species of farm animals we shall possess the scientific basis for a rational system of conserving to the utmost for man's use the energy which the studies of the chemist, the physicist, the botanist, the agronomist and the soil expert have taught the farmer how to accumulate in his crops. The investigations are, therefore, in reality a study of the conservation of the food supply, a problem even more fundamentally important than the conservation of our mines, forests or water powers, and one which vitally concerns the welfare not of the farmer alone but of the whole people.