In studying the results of previous investigations on undernutrition, it is of the greatest importance to note that there is a marked difference between complete fasting and chronic or partial inanition. The literature on complete fasting is fairly abundant and emphasizes sharply the fact that a complete fast is frequently accompanied by acidosis. This acidosis, it is believed, stimulates the cells of the fasting organism, producing a somewhat higher metabolism than might otherwise exist. Hence the subject of complete inanition is hardly touched upon in our citation of the literature.

1 Calculation by the Harris-Benedict multiple prediction formula (Harris and Benedict, Carnegie Inst. Wash. Pub. No. 279, 1919) gives 1,553 and 1,533 calories per 24 hours, respectively, i. e., 16 and 5.5 per cent above the found values.

Temporary complete absence of food from the stomach must not, however, be confused with complete fasting. As has been shown, the ingestion of food produces a definite effect upon metabolism. Any food in the stomach results in an increased heat production, food ingestion being second only to muscular work as a factor for producing an increase in the metabolism above basal, In looking over the literature on the subject of metabolism during undernutrition, one finds only too frequently that confusion has arisen from the fact that writers have included in the basal measurements the excess metabolism due to the stimulus of food. The instances are rare in which clear-cut evidence is given regarding the basal metabolism at different nutritional levels, for obviously an experiment which includes the activity incidental to food ingestion can throw but little light upon the actual basal requirements. It is quite probable that this practice is due in large part to the original conception of Rubner that when food is given below the maintenance requirement the so-called specific dynamic action of food does not appear.1 Modern experiments have shown that this is not the case and that the ingestion of food always stimulates metabolism.

For accurate comparative measurements it is possible to use only those values obtained when the subject is in complete muscular repose and when there is no food in the alimentary tract, i. e., with men usually 12 hours after the last meal, the so-called "post-absorptive condition." On the other hand, the use of basal values obtained in one, two, or more days of complete fasting is distinctly erroneous. All of the earlier discussions of the influence of partial nutrition upon the basal metabolism, which use basal values obtained on days of complete fasting, must therefore be considered as fundamentally incorrect.

The evidence on the gaseous exchange during undernutrition, as found in previous literature, is very conflicting. No better illustration of this uncertainty can be given than to point out the fact that writers may interpret exactly the same data in two strikingly different ways. Thus we have already shown that the data obtained by Falta, Grote, and Staehelin2 are, in our judgment, not justifiable as proof of a depression in metabolism. On the other hand, the metabolism measurements on Caspari!s vegetarian,3 according to Staehelin,4 show no reduction, while Zuntz1 and Caspari2 both specifically state that owing to the restlessness of the subject they are certain that the basal value has not been found. It thus follows that if the basal value on this man had been found, depressed metabolism would surely have been indicated.

1 Rubner, Zeitschr. f. Biol.. 1883, 19, p. 348.

2 Falta, Grote, and Staehelin, Beitr. a. chem. Physiol, u. Path., 1907, 9, p. 333.

3 Caspari, Arch. f. d. gea. Physiol., 1905, 109, p. 473.

4 Staehelin, Deutsch. med. Wochenschr., 1909, 35, p. 610.

If it were not for the specially clear evidence obtained from the recent experiments of Loewy and Zuntz, little of positive assurance could be derived from the literature. These experiments, taken in connection with the evidence presented by many of the earlier workers, indicate that with undernutrition there is a loss in weight and a tendency to a reduced metabolism. With a loss in body-weight, one would expect to find a lowering of the total metabolism, but with Loewy and Zuntz, and, to a certain extent, with Jansen's subjects, the metabolism per kilogram of body-weight was likewise distinctly lower during the reduced diet, thus showing that the basal metabolism was specifically lowered. This, they believe, was due to the loss of organic tissue. We thus have here a clear indication of a lower plane of nutrition. Such a change in nutritional level is also indicated by Rubner in his statement in enunciating his law of surface area that animals compared should be in the same state of nutrition.

On the basis of this evidence, one would expect to find, when examining the basal metabolism of normal men and women, that individuals of very low weight would have a low metabolism, both per kilogram of body-weight and per square meter of body-surface. In fact, data show clearly that thin people have a higher metabolism per kilogram of body-weight and as high a metabolism per square meter of body-surface as have fat people of the same age,3 for while Means4 contends that the heat per square meter of body-surface is the same with fat people as with the Du Bois normals, the obese usually give very low values per kilogram of body-weight. Furthermore, athletes (from whom presumably a large amount of body fat has been removed by training) show a higher metabolism than normal, although this is in large part due to the stimulus of cellular activity incidental to excessive muscular exercise. Considering individuals in general, therefore, the composition of the body appears to be of appreciable significance, and one may not state that 1 kg. of fat has the same heat-producing power as 1 kg. of active protoplasmic tissue. Consequently one would reason that when fat is lost, there would be a specific increase in the heat production per kilogram of body-weight. Quite the contrary was observed by Loewy and Zuntz.

On the other hand, aside from fat people, diabetics subsequent to the fasting treatment, and a man fasting 31 days, we have found no class of individuals having a low metabolism per kilogram of body-weight or per square meter of body-surface. While we are convinced that the so-called law of surface area is not so rigid in its application as its warmest advocates would like to believe, the numerous deviations from this law do not provide evidence as to any particular class or group of individuals with a low metabolism, although the high metabolism of athletes has been experimentally demonstrated.

1 Zuntz, Biochem. Zeitschr., 1913, 55, p. 342. 2 Caspari, Arch. f. d. ges. Physiol., 1905, 109, p. 564. 3Benedict, Journ. Biol. Chem., 1915, 20, p. 282. 4 Means, Journ. Med. Research, 1915, 32, p. 121.