Chapter III: The Balance of Nutrition (2)

By aid of the respiration calorimeter, many important questions in nutrition can be more or less accurately answered, especially such as relate to the total energy requirements of the body. The law of the conservation of energy obtains in the human body as elsewhere, and if we can measure with accuracy the total heat output, with any energy liberated in the form of work, and at the same time determine the total excretion of carbon dioxide, water, nitrogen, etc., together with the intake of oxygen, it becomes not only possible to ascertain the energy requirements of the body under different conditions, but, aided by data obtainable through study of the exchange of matter, we can draw important conclusions concerning the sources of the energy, _i. e._, whether from proteid, fat, or carbohydrate.

It is obvious that a man asleep, or lying quietly at rest, in the calorimeter, especially when he has been without food for some hours, furnishes suitable conditions for ascertaining the minimal energy requirements of the body. Under such conditions, bodily activity and heat output are at their lowest, and we are thus afforded the means of determining what is frequently called the basal energy exchange of the body. The following table taken from Magnus-Levy, and embodying results from many sources, shows the heat production during sleep, calculated for 24 hours, of various individuals of different body-weight and of different body surface.

I venture to present these individual results, rather than make a general statement simply, because it is important to recognize the fact that the basal energy exchange differs according to body-weight, extent of body surface, and the condition of the body. In the table, the results are arranged in the order of body-weight, and it is plain to see that the absolute energy exchange is greater with heavy persons than with light, yet the energy exchange does not increase in proportion to increase of body-weight. With a man of 83 kilos body-weight, the basal exchange is only 30–40 per cent higher than in a man of 43 kilos body-weight. In other words, the man of small body-weight has, per kilo, a much higher basal exchange than the heavier man. The energy exchange is more closely proportional to the extent of body surface than to weight.

+-------------+----------------+--------------+
| Body-weight | Total Calories | Calories per |
| of the | for 24 Hours. | Kilo of |
| Individual. | | Body-weight. |
+-------------+----------------+--------------+
| kilos | | |
| 43.2 | 1333 | 30.9 |
| 48.0 | 1214 | 25.3 |
| 50.0 | 1315 | 25.9 |
| 53.0 | 1527 | 28.8 |
| 55.0 | 1590 | 28.9 |
| 56.5 | 1519 | 26.8 |
| 57.2 | 1560 | 27.3 |
| 58.0 | 1510 | 26.0 |
| 62.5 | 1431 | 22.9 |
| 63.0 | 1418 | 22.5 |
| 63.0 | 1492 | 23.7 |
| 64.0 | 1656? | 25.8 |
| 64.9 | 1475 | 22.7 |
| 65.0 | 1498 | 23.0 |
| 65.0 | 1445 | 22.2 |
| 67.5 | 1608 | 23.8 |
| 67.5 | 1621 | 24.0 |
| 70.0 | 1661 | 23.7 |
| 70.0 | 1620 | 23.1 |
| 71.2 | 1787 | 25.1 |
| 72.6 | 1550 | 21.3 |
| 72.7 | 1657 | 22.8 |
| 73.0 | 1584 | 21.7 |
| 73.0 | 1630 | 22.4 |
| 75.6 | 1670 | 22.1 |
| 82.0 | 1556 | 19.0 |
| 82.7 | 2030? | 24.5 |
| 83.5 | 1670 | 20.0 |
| 88.3 | 2019? | 22.9 |
| 90.4 | 1773 | 19.6 |
+-------------+----------------+--------------+

As Richet has expressed it, the basal energy exchange is inversely proportional to the body-weight and directly proportional to the body surface. This is in harmony with the view advanced by v. Hösslin, “that all the important physiological activities of the body, including of course its internal work and the consequent heat production, are substantially proportional to the two-thirds power of its volume, and that since the external surface bears the same ratio to the volume, a proportionality necessarily exists between heat production and surface.”[35]

[35] See Armsby: Principles of Animal Nutrition, p. 368.

There are, however, many circumstances that modify, or influence, energy exchange. Thus, the taking of food, with all the attendant processes of digestion, assimilation, etc., involves an expenditure of energy not inconsiderable. This has been experimentally demonstrated on man by several investigators. With fatty food, Magnus-Levy found that his subject lying upon a couch, as completely at rest as possible, produced in the 24 hours 1547 calories when 94 grams of fat were eaten, and 1582 calories when 195 grams of fat were consumed. The increase of heat production over the basal energy exchange was 10 and 58 calories respectively. With a mixed diet, where proteid food is a conspicuous element, the increase in heat production is much more marked. Thus, in some experiments reported from Sweden the following data were obtained:[36]

[36] Taken from Armsby: Principles of Animal Nutrition, p. 383.

+---------+---------------------+------------------+
| Day. | Energy of the Food. | Heat Production. |
+---------+---------------------+------------------+
| | calories | calories |
| First | 4141 | .... |
| Second | 4277 | 2705 |
| Third | 0 | 2220 |
| Fourth | 0 | 2102 |
| Fifth | 0 | 2024 |
| Sixth | 0 | 1992 |
| Seventh | 0 | 1970 |
| Eighth | 4355 | 2436 |
| Ninth | 3946 | 2410 |
+---------+---------------------+------------------+

We see here an increase of 495 calories per day in heat production, due to metabolism of the food ingested. In other words, with a basal energy exchange of 2022 calories, the average of the five fasting days, energy equivalent to 495 calories was expended in taking care of the ingested food. It should be added, however, that the daily ration here was somewhat excessive, 4193 calories being considerably in excess of the requirements of the body. Finally, it should be stated that of the several classes of foods, proteids cause the greatest increase in metabolism and fats the least.

In studying heat production in the body under varying conditions, one of the important aids in drawing conclusions as to the character of the body material burned up is the respiratory quotient. This is the relationship, or ratio, of the oxygen absorbed to the oxygen of the carbon dioxide eliminated, viz., CO_{2}/O_{2}. Carbohydrates (C_{6}H_{12}O_{6}, C_{12}H_{22}O_{11}) all contain hydrogen and oxygen in the proportion to form water, H_{2}O, and in their oxidation they need of oxygen only such quantity as will suffice to oxidize the carbon (C) of the sugar to carbon dioxide (CO_{2}). Carbohydrates, starch and sugars, have a respiratory quotient of 1.00. Fat, on the other hand, has a respiratory quotient of 0.7, and proteid, 0.8. Hence, it is easy to see that the respiratory quotient will approach nearer to unity as the quantity of carbohydrate burned in the body is increased. Similarly, the respiratory quotient will grow smaller the larger the amount of fat burned up. Practically, we never find a respiratory quotient of 1.0 or 0.7, because there is always some oxidation of proteid in the body. If, by way of illustration, we assume that the energy of the body under given conditions comes from proteid to the extent of 15 per cent, while the remaining 85 per cent is derived from the oxidation of carbohydrate, the respiratory quotient will be 0.971. If, however, the 85 per cent of energy comes from fat, the respiratory quotient will change to 0.722. In the resting body, as in the early morning hours, after a night’s sleep and before food is taken, the respiratory quotient is generally in the neighborhood of 0.8. When, however, as sometimes happens, the quotient at this time of day approaches 0.9, it must be assumed that sugar is being burned in the body, presumably from carbohydrate still circulating from the previous day’s intake.

As can easily be seen, any special drain upon either fat or carbohydrate in the processes of the body will be indicated at once by a corresponding change in the respiratory quotient. This we shall have occasion to notice later on, in considering the source of the energy of muscle contraction. Further, the respiratory quotient will naturally change in harmony with transformations in the body which involve alterations in oxygen-content, without the oxygen of the inspired air being necessarily involved; as in the formation of a substance poor in oxygen, such as fat, from a substance rich in oxygen, such as carbohydrate. Moreover, the reversal of this reaction, as in the formation of sugar from proteid with a taking on of oxygen, will produce a corresponding effect upon the respiratory quotient. As Magnus-Levy has clearly pointed out, in the formation of fat from carbohydrate, carbon dioxide is produced in large amount without the oxygen of the inspired air being involved at all. In such a change, 100 grams of starch will yield about 42 grams of fat, while at the same time 45 grams of carbon dioxide will be produced. This might cause the respiratory quotient to rise as high as 1.38. Again, in the formation of sugar from proteid, the respiratory quotient may sink very decidedly, the changes involved being accompanied by a taking on of oxygen from the air, without, however, any corresponding increase of carbon dioxide in the expired air. Assuming a manufacture of 60 grams of dextrose from 100 grams of proteid, _i. e._, from the non-nitrogenous moiety of the proteid molecule, a respiratory quotient of 0.613 would be possible. Thus, a diabetic patient, living upon a carbohydrate-free diet, consuming only proteid and fat, may show a respiratory quotient of 0.613–0.707. These illustrations will suffice to show how chemical alterations taking place in the body, involving transformations of proteid, fat, and carbohydrate of the tissues and of the food, may produce alterations in the respiratory quotient without necessarily being directly connected with intake of oxygen or output of carbon dioxide through the lungs; and how, conversely, the respiratory quotient becomes a factor of great significance in throwing light upon the character of the nutritive changes taking place in the body.

Among the various conditions that influence the energy exchange of the body, muscle work stands out as the most conspicuous. It needs no argument to convince one that all forms of muscular activity involve liberation of the energy stored up in the tissues of the body; and consequently that all work accomplished means chemical decomposition, in which complex molecules are broken down into simple ones with liberation of the contained energy, the energy exchange being proportional to the amount of work done. As we have seen, the basal energy exchange of the normal individual is ascertained by studying his heat production while at rest--best during sleep--without food, when involuntary muscle activity and heat production are at their lowest. The maximum energy exchange is seen in the individual at hard muscular work. Heat production is then at its highest, as can be ascertained by direct calorimetric observation; or, by studying the output of excretory products, which measure the extent of the oxidative processes from which comes the energy for the accomplishment of the work. As an illustration of the general effect of muscular work on the energy exchange of the body, we may cite a summary of some results reported by Atwater and Benedict,[37] the figures given being average results, from several individuals, and covering different periods of time. Though not strictly comparable in all details, they are sufficiently so to illustrate the main principle.

[37] Atwater and Benedict: Experiments on the Metabolism of Matter
and Energy in the Human Body 1900–1902. Bulletin No. 136, Office of
Experiment Stations, U. S. Department of Agriculture, 1903, p. 141.

HEAT GIVEN OFF BY BODY, INCLUDING FOR WORK EXPERIMENTS THE HEAT EQUIVALENT OF THE EXTERNAL MUSCULAR WORK.

+----------------+--------+---------------------------------------+--------+
| | Total | Rates per Hour. | |
| | Amount +-------------------+-------------------+ Average|
| Kind of | of Heat| Day Periods. | Night Periods. | for |
| Experiment. | in 24 | | | 24 |
| | Hours. +---------+---------+---------+---------+ Hours. |
| | |7 A.M. to|1 P.M. to|7 P.M. to|1 A.M. to| |
| | | 1 P.M. | 7 P.M. | 1 A.M. | 7 A.M. | |
+----------------+--------+---------+---------+---------+---------+--------+
| |calories| calories| calories| calories| calories|calories|
|Rest experiments| 2262 | 106.3 | 104.4 | 98.3 | 67.9 | 94.3 |
+----------------+--------+---------+---------+---------+---------+--------+
|Work experiments|} | | | | | |
| Heat eliminated|} 4225 | 231.7 | 235.6 | 118.1 | 78.4 | 166.6 |
| | | | | | | |
|Heat equivalent |} | | | | | |
| of external |} 451 | 58.5 | 56.8 | ... | ... | ... |
| muscular work |} | | | | | |
+----------------+--------+---------+---------+---------+---------+--------+
| Total | 4676 | 290.2 | 292.4 | 118.1 | 78.4 | 194.8 |
+----------------+--------+---------+---------+---------+---------+--------+

The work done in these experiments was on a stationary bicycle in the calorimeter, and the heat equivalent was calculated from measurements made by an ergometer attached to the bicycle. We are not concerned here with details, but simply with the general question of the influence of muscular work upon the energy exchange of the body. We note that the work of the day periods, 7 A. M. to 7 P. M., resulted, in the several cases brought together under the average figures, in an increased heat production amounting to more than 100 per cent. Further, we observe that in the body, as in all machines, only a fraction of the energy liberated by the accelerated chemical decomposition, or oxidation, was manifested as mechanical work, the larger part by far being heat eliminated and lost. Thus, Zuntz has found that, in man, about 35 per cent of the extra energy of the food used in connection with external muscular work is available for that work. This, however, shows a noticeably higher degree of efficiency than is generally obtainable by the best steam or oil engines. Lastly, attention may be called to the fact that after the work of the day was finished at 7 P. M., the next period of six hours still showed an accelerated metabolism, as contrasted with what took place during absolute rest.

As bearing upon the exchange of matter in the body in connection with muscular work, and as showing the relationship which exists here between energy exchange and exchange of matter, we may quote a few data relating to the elimination of carbon dioxide; remembering that this substance represents particularly the final oxidation product in the body of carbonaceous materials, such as fat and carbohydrate. The following data, taken from Atwater and Benedict,[38] being results of experiments upon the subject “J. C. W.,” are of value as showing the variations in output of carbon dioxide that may be expected under the conditions described:

[38] Loc. cit., pp. 130 and 131.

+------------------+---------+---------+-----------+---------+----------+
| | | | | | Extra |
| | Rest Ex-| Rest Ex-| Work Ex- | Work Ex-| Severe |
| Period. |periments|periments| periments |periments| Work |
| | without | with |with Carbo-| with |Experiment|
| | Food. | Food. | hydrate |Fat Diet.| with |
| | | | Diet. | |Fat Diet. |
+------------------+---------+---------+-----------+---------+----------+
| | grams | grams | grams | grams | grams |
| 7 A.M. to 1 P.M. | 189.6 | 230.4 | 694.0 | 642.3 | 907.0 |
| 1 P.M. to 7 P.M. | 172.6 | 232.0 | 705.6 | 634.8 | 821.3 |
| 7 P.M. to 1 A.M. | 167.2 | 196.6 | 260.1 | 230.3 | 842.7 |
| 1 A.M. to 7 A.M. | 146.7 | 153.1 | 161.1 | 157.6 | 502.6 |
+------------------+---------+---------+-----------+---------+----------+
|Total for 24 hours| 676.1 | 812.1 | 1820.8 | 1665.0 | 3073.6 |
+------------------+---------+---------+-----------+---------+----------+

In considering these figures bearing on the output of carbon dioxide under the conditions specified, we note at once a correspondence with the total energy exchange, as indicated in the preceding table. As previously stated, we are at present dealing simply with generalities, and the important point to be observed here is that muscular work--7 A. M. to 7 P. M.--in the work experiments, increases enormously the output of carbon dioxide. We see clearly emphasized a connection between the total energy exchange of the body, as expressed in calories or heat units, and the oxidation of carbonaceous material, of which carbon dioxide is the natural oxidation product. We note that on the cessation of work--7 P. M. to 7 A. M.--the output of carbon dioxide tends to drop back to the level characteristic of the corresponding period in rest, with or without food. In the experiment with “extra severe muscular work,” the results are different simply because here the subject worked sixteen hours, necessitating a portion of the work being done at night-time. Finally, it should be mentioned that the differences in output of carbon dioxide in these experiments are somewhat greater than in many experiments of this type, although all show the same general characteristics. This may be explained, as stated by the authors from whom the data are taken, “by the fact that J. C. W. was a larger and heavier man than any of the others; that the differences in diet were wider, and that the amounts of external muscular work were larger in these experiments than in those with the other subjects.”

If we pass from experiments of this type, conducted in a calorimeter, to those cases where competitive trials of endurance are held by trained athletes, _i. e._, where external muscular activity is pushed to the extreme limit, we then see even more strikingly displayed the effect of work in increasing the energy exchange of the body. One of the best illustrations of this type of experiment is to be found in the observations made in connection with the six-day bicycle race held in New York City, at the Madison Square Garden, in December, 1898.[39] The observations in question were made upon three of the athletes, one of whom withdrew early in the fourth day, while the others continued until the close of the race--142 consecutive hours--winning the first and fourth places, respectively. The following table gives the computation of energy of the material metabolized, exclusive of body-fat lost:

[39] See W. O. Atwater and H. C. Sherman: The effect of severe
and prolonged muscular work on food consumption, digestion, and
metabolism. Bulletin No. 98, Office of Experiment Stations, U. S.
Department of Agriculture.

+------------+-------------+--------------+-------------+
| Subject. | Duration of | Total Energy | Average per |
| | Experiment. | Metabolized. | Day. |
+------------+-------------+--------------+-------------+
| | days | calories | calories |
| Miller | 6 | 28917 | 4820 |
| Albert | 6 | 36441 | 6074 |
| Pilkington | 3 | 13301 | 4464 |
+------------+-------------+--------------+-------------+

Miller, the winner of the race, who averaged a daily energy exchange of 4820 calories, rode 2007 miles during the week, and finished the race without physical or mental weakness resulting from the fatigue and strain. During the first five days, he rode about 21 hours a day and slept only 1 hour. Albert, who weighed a few pounds less than Miller, covered 1822 miles in 109 hours, with an average daily exchange of 6074 calories. We may add a table (on the following page) showing the balance of income and outgo of nitrogen in these three subjects, as being of general interest in this connection. The figures given are averages per day.

+----------+-----+---------------------------------+-------------------+
| |Dura-| Income in Food. | Nitrogen. |
| Subject. |tion +-----+-----+------+--------+-----+------+------+-----+
| | of | | |Carbo-| | | | In | |
| |Exp. | Pro | Fat.| hy- | Fuel | In | In |Excre-|Loss.|
| | |teid.| |drate.| Value. |Food.|Urine.|ment. | |
+----------+-----+-----+-----+------+--------+-----+------+------+-----+
| |days |grams|grams|grams |calories|grams|grams |grams |grams|
|Miller | 6 | 169 | 181 | 585 | 4770 | 29.4| 36.2 | 1.8 | 8.6 |
|Albert | 6 | 179 | 198 | 559 | 6095 | 29.1| 33.7 | 2.5 | 7.1 |
|Pilkington| 3 | 211 | 178 | 509 | 4610 | 36.0| 38.9 | 2.2 | 5.1 |
+----------+-----+-----+-----+------+--------+-----+------+------+-----+

The special significance of these data, as bearing upon the topic under discussion, is that apparently all three of the subjects were drawing in a measure upon their body material. As stated by Atwater and Sherman, Pilkington lost per day 5.1 grams of nitrogen; that is to say, the total nitrogen excreted exceeded the total nitrogen of the food by 5.1 grams per day, corresponding to 33 grams of proteid, which must have been drawn from the supply in the body. If we assume that lean flesh contains 25 per cent of proteid, this would mean about 4-3/4 ounces per day. The other two subjects, Miller and Albert, lost from the body per day 8.6 grams and 7.1 grams respectively of nitrogen, which would imply a loss of about 54 grams and 44 grams of body proteid respectively, or 8 ounces and 6-1/4 ounces of lean flesh per day. It is evident, therefore, that none of the three subjects consumed sufficient food to avoid loss of body proteid, under the existing conditions of muscular activity. Indeed, it may be noted in Miller’s case that the average fuel value of the food per day was 4770 calories, while the average expenditure of energy per day was 4820 calories. We should naturally expect, however, that any small deficiency in fuel value would be made good by a call upon body fat. “Why the body should use its own substance under such circumstances is a question which at present cannot be satisfactorily answered. The fact that such was the case, each of the contestants who finished the race consuming during the period body protein equivalent to 2 or 3 pounds of lean flesh, and that no injury resulted therefrom, would seem to indicate that these men had stores of protein which could be metabolized to aid in meeting the demands put upon the body by the severe exertion, without robbing any of the working parts, and at the same time relieving the system of a part of the labor of digestion. Possibly, the ability to carry such a store of available protein is one of the factors which make for physical endurance.”[40] This possibility we shall have occasion to discuss in another connection. At present, the facts presented are to be accepted as accentuating the general law that the energy exchange of the body, everything else being equal, is increased proportionally to increase in the extent of external muscular activity. It may be noted that Albert, who did considerably less work than Miller, showed a much larger exchange of energy than the latter athlete. This, however, is to be connected with the fact that his fuel intake was 1300 calories larger per day than Miller’s; in other words, the conditions were not equal. This fact also calls to mind the observations of Schnyder,[41] who, studying the relationship between muscular activity and the production of carbon dioxide, maintained that the quantity of this excretory product formed depends less upon the amount of work accomplished than upon the intensity of the exertion; efficiency in muscular work varying greatly with the condition of the subject, and his familiarity with the particular task involved.

[40] Atwater and Sherman. Loc. cit., p. 51.

[41] L. Schnyder: Muskelkraft und Gaswechsel. Zeitschrift für
Biologie, Band 33, p. 289.

From what has been said, it is obvious that oxygen consumption, as well as output of carbon dioxide, must vary enormously with variations in the muscular activity of the body. The one important factor influencing the quantities of oxygen and carbon dioxide exchanged in the lungs, _i. e._, the extent of the respiratory interchange, is muscular activity; and since, as we have seen, carbonaceous material is the substance mainly oxidized in muscle work, it follows, as carbon dioxide is excreted principally through the lungs, that the respiratory interchange becomes in good measure an indicator of the extent of chemical decomposition incidental to external work. If we recall that man, on an average, at each inspiration draws in about 500 cubic centimeters of air (30 cubic inches), and that for the 24 hours he averages 15 breaths a minute, it is easy to see that in one minute the average man will inspire 7.5 litres of air, or 450 litres an hour, with a total of 10,800 litres for the entire day, which is equivalent to about 380 cubic feet. This would be a volume of air just filling a room 7-1/3 feet in length, width, and height. Inspired air loses to the body 4.78 volumes per cent of oxygen, while expired air contains an excess of 4.34 volumes per cent of carbon dioxide. In muscular work, respiration is increased in frequency and in depth. The volume of air exchanged in the lungs during severe labor may be increased sevenfold, while oxygen consumption and carbon dioxide excretion are frequently increased 7–10 times. The following figures, being values for one minute, show the effect on oxygen consumption of walking on a level and climbing, the subject being a man of 55.5 kilos body-weight:[42]

[42] G. Katzenstein: Ueber die Einwirkung der Muskelthätigkeit auf
den Stoffverbrauch des Menschen. Pflüger’s Archiv für die gesammte
Physiologie, Band 49, p. 330. Also Magnus-Levy: v. Noorden’s Handbuch
der Pathologie der Stoffwechsel, p. 233.

+------------------+----------------------------------------+-----------+
| |Oxygen Consumption in Cubic Centimeters.| |
| +---------+------------------------------+ |
| | | After Deducting Value | |
| Form of Work. | | for Rest. |Respiratory|
| | Total. +-----------+------------------+ Quotient. |
| | | | For Each | |
| | | Total. | Kilo of Moving | |
| | | | Weight. | |
+------------------+---------+-----------+------------------+-----------+
|Standing at rest | 263.75 | .... | .... | 0.801 |
|Walking on a level| 763.00 | 499.25 | 8.990 | 0.805 |
|Climbing | 1253.20 | 989.45 | 17.819 | 0.801 |
+------------------+---------+-----------+------------------+-----------+

Remembering that these figures represent the oxygen consumption for only one minute of time, it is easy to see the striking effect of moderate and vigorous exercise on respiratory interchange. Simply walking along a level suffices to increase the consumption of oxygen threefold over what occurs when the body stands at rest. When the more vigorous exercise attendant on lifting the body up a steep incline is attempted, most striking is the great increase in the amount of oxygen consumed. We thus see another forcible illustration of the influence of muscular activity upon the exchange of matter in the body, and a further confirmation of the statement, so many times made, that oxidation--especially the oxidation of fats and carbohydrates by which large quantities of heat are set free, easily convertible into mechanical energy--is a primary factor in the metabolic processes, by which the machinery of the living man is able to work so efficiently.

Finally, we cannot avoid the conclusion that the outgoings of the body, in the form of matter and energy, are subject to great variation, incidental to the degree of activity of the day or hour. The ordinary vicissitudes of life, bringing days of physical inaction, followed perhaps by periods of unusual activity; changes in climatic conditions, with their influence upon heat production in the body; alterations in the character and amount of the daily dietary, etc.,--all seemingly combine as natural obstacles to the maintenance of a true nutritive balance. Outgo, however, must be met by adequate amounts of proper intake if there is to be an approach toward a balance of nutrition. In some way the normal, healthy man does maintain, approximately at least, a condition of balance; not necessarily for every hour or for every day, but the intake and outgo if measured for a definite period, not too short, say for a week or two, will be found to approach each other very closely. Body equilibrium and approximate nitrogen balance may be reasonably looked for, as well as a balance of total energy, in the case of a healthy man leading a life which conforms to ordinary physiological requirements. The man who, on the other hand, consciously or unconsciously, continues an intake way beyond the outgo, whose daily income of nitrogen and total fuel value far exceeds the requirements of his body, obviously lives with an accumulating plus balance, which ordinarily shows itself in increasing body-weight and with a storing away of fat.

Equally conspicuous is the effect of an inadequate income of proper nutriment; a food supply which persistently fails to furnish the available nitrogen and total energy value called for by the body under the conditions prevailing, will inevitably result in a minus balance, which, if continued too long, must of necessity tax the body’s store to the danger limit. At the same time, the well-nourished individual, without being unduly burdened by a bulky store of energy-containing material, is always supplied with a sufficient surplus to meet all rational demands, when from any cause the intake fails, for brief periods of time, to be commensurate with the needs of the body. It is reasonable to believe, however, that in the maintenance of good health, and the preservation of a high degree of efficiency, the body should be kept in a condition approaching a true nutritive balance.