It has been said, notably by Munk, that in dogs fed for some time on a low proteid diet there is a diminished power of absorption from the intestinal tract, associated with weakened digestion. If it is true that a lowered proteid intake results in a diminished utilization of the ingested food, that efficiency in the digestion and absorption of foodstuffs is impaired, it can only be interpreted as meaning that some injurious influence has been exerted on the epithelial cells of the intestine or the adjacent gland cells. We have, however, failed to find any evidence of deleterious action in the dogs that we have experimented with, where due regard was paid to maintaining a diet suitable for the physiological needs of the body. In the experiments that we have cited, both nitrogen intake and the fuel value of the food per day were lower than in Munk's experiments, but the utilization of fat and proteid was not sensibly affected. The following tables give the results with ten dogs (including the six dogs already described) for lengths of time ranging from seven to twelve months, the periods indicated being each of ten days' duration and occurring once each month. In the first table, the utilization of fat is shown, the figures given being based on determinations of the amount of fat contained in the excrement. Knowing the amount of fat in the daily food and the amount which passed through the intestine, it is easy to calculate the percentage of fat utilized.

Utilization Of Fat In Percentages

It is perfectly plain from these results that there was no falling off in the utilization of fat; the percentage amount digested and absorbed, as in dogs 3 and 4, was just as large at the end of the twelve months' experiment as at the beginning. Clearly, a so-called low nitrogen intake with dogs does not lead to any loss of power in the utilization of the fat of the food. This being so, it is equally clear that the arguments based on Munk's results in this direction, and applied to man, are without adequate foundation.

Utilization Of Nitrogen In Percentages

The figures in the above table were obtained by determining the amount of nitrogen in the dried excrement from the animals, i. e. the amount that passed through the intestine unchanged;1 and knowing the content of nitrogen in the daily food, the percentage of unabsorbed nitrogen was then easily calculated, after which by simple subtraction the percentage of utilized nitrogen was found. At first glance, it would appear that as the experiments proceeded utilization of nitrogen was less complete. In a sense, this was true, but it was not connected with any impairment of the digestive or absorptive powers of the intestine. It must be remembered that in the earlier periods a larger proportion of the ingested nitrogen was in the form of readily digestible meat, but as the latter was reduced in amount larger proportions of vegetable food were introduced in order to maintain the desired fuel value, and consequently the percentage of non-absorbable nitrogen was increased. The well-known difference in the availability of animal and vegetable proteid has already been referred to in other connections; a difference due not so much to any inherent quality in the digestibility of the two forms of proteid as to the presence of cellulose and other material in the vegetable food which retards in some measure the action of the digestive juices. To this cause must be ascribed the slight falling off in the utilization of nitrogen noticeable in most of the experiments. If, however, the figures are compared with those usually obtained on a diet largely vegetable in nature, it will be seen that the utilization of nitrogen by these dogs was in no sense abnormal.

1 There is an unavoidable error here, since the excrement contains not only undigested food, but also contains some nitrogenous matter derived from the secretions of the intestine, etc.

These experiments on the influence of a low proteid diet on dogs, as a type of high proteid consumers, taken in their entirety, afford convincing proof that such animals can live and thrive on amounts of proteid and non-nitrogenous food far below the standards set by Munk and Rosenheim. The deleterious results reported by these investigators were not due to the effects of low proteid or to diminished consumption of non-nitrogenous foods, but are to be ascribed mainly to non-hygienic conditions, or to a lack of care and physiological good sense in the prescription of a narrow dietary not suited to the habits and needs of this class of animals. Further, it is obvious that the more or less broad deductions so frequently drawn from the experiments of Munk and Rosenheim, especially in their application to mankind, are entirely unwarranted and without foundation in fact. Our experiments offer satisfying proof that not only can dogs live on quantities of proteid food per day smaller than these investigators deemed necessary, and with a fuel value far below the standard adopted by them; but, in addition, that these animals are quite able on such a diet to gain in body-weight and to lay by nitrogen, thereby indicating that even smaller quantities of food might suffice to meet their true physiological requirements.

The results of these experiments with dogs, which we have recorded in such detail, are in perfect harmony with the conclusions arrived at by our experiments and observations with man, and serve to strengthen the opinion, so many times expressed, that the dietary habits of mankind and the dietary standards based thereon are not always in accord with the true physiological requirements of the body. If these views are correct, and the facts presented seemingly indicate that they are, it is time for enlightened people to give heed to such suggestions, that their lives may be ordered more nearly in accord with the best interests of the body. Physiological economy in nutrition is not a myth, but a reality full of promise for the welfare of the individual and of the community in general. Ignorance on dietary matters should give place to an intelligent comprehension of the body's needs, and an adequate understanding of how best to meet the legitimate demands of the system for nourishment under given conditions of life. It is said that more than half the earnings of the working people of this country is spent for food. Here, we have suggested another form of economy as worthy of consideration; less important perhaps than that which relates to health and strength, but still calling for thoughtful attention. We cannot afford to be ignorant of these things; we must have definite knowledge of the actual facts, and these can only be obtained by careful research and investigation.

As a prominent writer on nutrition has well said, "The health and strength of all are intimately dependent upon their diet. Yet most people understand very little about what their food contains, how it nourishes them, whether they are economical or wasteful in buying and preparing it for use, and whether or not the food they eat is rightly fitted to the demands of their bodies. The result of this ignorance is great waste in the purchase and use of food, loss of money, and injury to health " (Atwater). We all recognize the general force and truth of this statement, but there is a surprising lack of appreciation of the full significance of what is involved thereby. If it is true that the demands of the body for pro-teid food - which of all foods is the most expensive - are fully met by an amount equal to one-half that ordinarily consumed, and that health and strength are more satisfactorily maintained thereby, it is easy to see how the acquisition of dietary habits leading to consumption of food in harmony with physiological needs will result in a fruitful twofold economy; viz., economy in expenditure, and of still greater moment, economy in the activities of the body by which food and its waste products are cared for.