Many of the researches on undernutrition in the earlier literature were made with animals, and some were carried out under pathological conditions. In collecting data regarding the previous investigations on undernutrition, the studies dealing solely with the loss of nitrogen have been purposely omitted, for only in rare instances have there been satisfactory determinations of the balance of nitrogen intake and output for indicating a true gain or loss to the body. The total nitrogen outgo, i. e., the nitrogen in the urine and feces, may be accurately determined without extraordinary analytical procedure, but this tells only half the story and must be supplemented by data regarding the intake. The difficulty of sampling and analyzing mixed diets to secure the total nitrogen of intake is obvious; computed values have, at best, but little significance. Moreover, the nitrogen data are in many of the studies complicated by distinct pathological conditions, thus excluding them from special consideration in a study of the influence of undernutrition on normal healthy people. It seems best, therefore, to disregard the literature bearing upon the subject of the loss of nitrogen due to undernutrition and to confine the discussion of the previous findings solely to the influence of undernutrition upon the gaseous metabolism.

Pettenkofer And Voit, 1871

The importance of studying animals in different stages of nutrition was early recognized by Pettenkofer and Voit,1 who made observations in which 500 to 2,500 grams of meat were fed daily to a dog weighing approximately 35 kg. The smaller portion of food, which corresponds more specifically to undernutrition, was continued for approximately 6 weeks. At first sight it appears as if an experiment of this type would throw definite light upon the demands of the body while on a low nutritional plane. The experimental technique, however, which unfortunately was followed by a number of later observers, involved feeding the animal with meat, placing it at once inside the respiration chamber, and then making observations on the respiratory products in 24-hour periods. It is to be regretted that the excellent method frequently employed by Pettenkofer and Voit of separating their experimental period into day and night periods was not here used, for it is undoubtedly true that during the first hours of the day the metabolism was greatly stimulated by the ingestion of meat, the stimulation being approximately proportional to the amounts of meat ingested. The metabolism as measured, therefore, was not basal metabolism, but basal metabolism plus the stimulus of meat. The authors note that there was a distinct falling off in the metabolism when the smaller quantities of meat were given, 500 grams of meat representing scarcely half the dog's requirements. While Pettenkofer and Voit have not specifically discussed in detail the undernutritional stage of this series of experiments, their data are referred to and in a certain sense recalculated by Rubner.1 In discussing these and some other experiments Rubner recognizes that, in addition to the loss in body substance produced by acute or prolonged hunger, the heat-production usually decreases in proportion to the decrease in mass, but points out the possibility of individuality. In Pettenkofer and Voit's experiments, while there was no measurable loss in carbon-dioxide excretion per kilogram of body-weight during the period of undernutrition, in which the body-weight varied from 34.4 to 30.0 kg., there was a much greater heat-production, as measured by the carbon-dioxide output, with a diet of 1,500 grams of meat than with 1,000 grams. The fact that the actual basal metabolism was not measured makes it difficult to interpret these experiments as evidence of a decrease in the basal metabolism due to undernutrition.

1 Pettenkofer and Voit, Zeitschr. f. Biol., 1871, 7, p. 433.

Klemperer, 1889

Although based primarily upon nitrogen measurements and body-weight rather than upon the metabolism, Klem-perer's2 conception of the adjustment of the body to high or low diets is the first clearly formulated. In his celebrated experiment on a tailoress, Klemperer, arguing from the fact that body nitrogen was in equilibrium and that consequently the calories must have been in equilibrium, maintained that this individual could, when resting in bed, subsist upon 18 calories per kilogram per 24 hours. Both experiment and conclusion have been adversely criticized by von Noorden,3 but Klemperer was the first to indicate "die Moglichkeit und Wahr-scheinlicfckeit verringerten Energieumsatzes" or "die Lehre von der Anpassung des Umsatzes an die gereichte Kost."4

Lehmann, Mueller, Munk, Senator, And Zuntz, 1893

The classic experiments made by Lehmann, Mueller, Munk, Senator, and Zuntz5 on two fasting men must be interpreted in the light of the present day knowledge of the influence of fasting upon metabolism. Zuntz and Lehmann concluded, because the heat production of the subject Breithaupt after the fast was less, even with a larger diet, than before the fast (24.8 as compared with 27.3 calories per kilogram per 24 hours), that with certain conditions the undernourished body may use foodstuffs more economically than a well-nourished body, but emphasize the fact that further information is desirable. We now know that fasting per se depresses the metabolism. The ingestion of food first offsets this depression, then stimulates the metabolism to higher activity; hence these experiments are not clear evidence on undernutrition and serve only to point out the error of using the last day of fasting for a base-line.

1 Rubner, Gesetse dee Energieverbrauchs bei der Ernahrung, Leipaic, 1902, pp. 296-297.

2 Klemperer, Zeitschx. f. klin. Med., 1889,16, p. 597.

3 von Noorden, Metabolism and practical medicine, 2, Pathology, Chicago, 1907, foot-note 1, p. 5.

4 Magnus-Levy, Zeitschr. f. klin. Med., 1906,60, p. 203.

5 Lehmann, Mueller, Munk, Senator, and Zunts, Arch. f. path. Anat. u. Physiol., 1893, 131, Supphft., p. 1.