TISSUE RESPIRATION, GROWTH, AND BASAL METABOLISM LUDWIG VON BERTALANFFY AND W. J. PIROZYNSKI 1 Department of Biology, Faculty of Medicine, University of Ottaiva, Canada It is a phenomenon general in mammals and other classes of the animal king-dom that metabolic rate per unit weight decreases with increasing body size. This is expressed in the surface rule of Rubner who stated that metabolic rate decreases per unit weight, but is constant per unit surface. More recent investigations (Brody, 1945 ; Kleiber, 1947) indicate that interspecifically, i.e., comparing mature animals of different species, basal metabolic rate in mammals is proportional rather to a % power of weight than to surface or the % power of weight. Intraspecifi-cally, i.e., comparing animals of different body size within the same species, the sur-face rule applies to the general trend of the size-metabolism relation in rats, al-though qualifications have to be made in detail (Bertalanffy, Miiller and Racine, unpublished data). These complications, however, do not alter the fundamental fact of the decrease in weight-specific metabolic rate with increasing body size. However, we do not have a satisfactory explanation for this phenomenon. The basic alternative seems to be whether the dependence of metabolism on body size is based upon cellular or organisiuic factors. It may be due to intrinsic differences in the metabolism of the cells of smaller and larger individuals which will show up also in isolated tissues ; or it may be due to regulative factors lying in the organism as a whole. There may be also a combination of both. Earlier work on the relation between tissue metabolism and body size (re-viewed by Kleiber, 1947) is contradictory. Terroine and Roche (1925), and, in-dependently, Grafe (1925; Grafe, Reinwein and Singer, 1925), stated that the metabolic rate per unit weight of homologous tissues in vitro is essentially the same for small and large animals, although basal metabolic rate per unit weight in vivo decreases systematically with increasing body size. Grafe assumed that the meta-bolic rate of tissue in situ is checked by central regulators, mainly the nervous and endocrine system. On the other hand, LeBreton and Kayser (1926; Kayser, LeBreton and Schaeffer, 1925), and Borger and Groll (1926) reported variation of the respiration rate of tissues with increasing body size, in individuals of the same species as well as in different species. This earlier work is open to criticism, and Grafe et al.'s calculations, in particular, were based upon erroneous assumptions (cf. Field ct al, 1939). More recent results, however, are also contradictory. According to Field et al. (1939) the summated tissue respiration (i.e., metabolic rate in vitro per unit fresh weight, multiplied by the weight of the respective organ, and summated over 20 main organs) amounts to 66% of the basal metabolic rate of the rat, and, if allowance is made for minimal functional activity (muscle tone, cardiac, respira-tory, smooth muscle, secretory function), even for 89% of the respiration of the intact animal. The authors conclude that basal metabolism is the arithmetic sum 1 This work is supported by a grant from the National Cancer Institute of Canada. 240
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