V GROWTH IN TIME OF THE TOTAL ORGANISM 187 



Jehl, 1952); teleost brain (Vernberg and Gray, 1953); and rat testes (Homma, 

 1 953 5 with a characteristic break in the allometric Une at puberty; cf. p. 2i8f.). 

 Similarly, Fried and Tipton (1953) did not find a decrease in the content of 

 respiratory enzymes. The data, in intraspecific comparison of rats, on cytochrome 

 oxidase (Kunkel and Campbell, 1952) correspond well with the Q02 ^^*^^ 

 (Bertalanffy and Pirozynski, 1953; Bertalanffy and Estwick, 1953). There is a 

 slight positive allometry (increase of values per mg) of both cytochrome oxidase 

 activity and Qq i'^ biain and kidney and slight decrease of both with body size 

 in the liver; a discrepancy is found in skeletal muscle of larger rats (a = — 0.24 

 for cytochrome oxidase as against — 0.065 ^^r QoJ, but here Kunkel and Camp- 

 bell's data have the least statical significance (p = — 0.69 as against near unity 

 in the other series). 



It appears, therefore, that differences in enzymatic activity and Q02 ^^ tissues 

 are determined genetically, and are species-specific; differences in animals of the 

 same species and different weight vary in different tissues or are inconspicuous. 



Extensive investigations on the relations between Qoj^ body size, and temperature were 

 conducted by Locker (1958a) on frogs (intraspecifically: 1.5-70 g, and winter and summer 

 frogs), and including other amphibian and reptilian species (interspecifically). Qo, of frog 

 liver vs. body size shows a break in the allometric regression line at ca. 25 g body weight; 

 with increasing temperature, the difference of a for smaller and larger animals disappears. 

 In contrast, Qoj of frog epidermis vs. body weight shows a continuous regression, a being 

 K — 0.33 (surface rule). The dependence of Q02 01^ body size further varies with different 

 bases of comparison (dry weight or mg N), and glycogen content (Locker and Doneff, 1958). 

 The activation energy (fj.) of tissue respiration of both frog liver and epidermis (Locker, 

 1958a) and liver of mammals (Locker, 1958c) decreases systematically with body size. 

 Locker's investigations show that the relations between body size, Qo^, temperature, 

 substratum of respiration, etc., are by no means simple. Bertalanffy's "metabolic types" 

 (p. i9off.) express certain master reactions in the complex correlations between metabolism 

 and growth. 



2. Similar considerations apply to the hypothesis (Krebs, 1950) that the 

 reduction of metabolic rate with increasing body size is due to a decrease of Qq^ 

 of the tnusculature. In intraspecific comparison of rats, Q_q^ of skeletal muscle only 

 slightly decHnes with increasing body size (Bertalanffy and Estwick, 1953), 

 although in mice the reduction of muscular Qo, is similar to that of weight- 

 specific basal rate (Estwick, 1953). Interspecifically, this value is similar in adult 

 mice and rats (Bertalanffy and Estwick, 1953). 



{b) So we have to assume that the reduction of metaboUc rate in intraspecific 

 comparison is due to or ganismic factors which, within the intact organism, regulate 

 the respiration of the tissues the sum total of which is the metabolism of the entire 

 animal, but do not necessarily show up in isolated tissues as used for Warburg 

 determinations (Bertalanffy and Pirozynski, 1951; Schmidt-Nielsen, Bertalanffy, 

 and Pirozynski, 195 1). The nature of these limiting factors is not definitely 

 established and the factors usually contemplated do not offer a satisfactory 

 explanation. 



3. The most familiar one has already been mentioned, namely, thermoregulation. 

 Energy expense for thermoregulation forms a considerable part of total meta- 

 bolism in homeothermic animals. However, this explanation cannot be general 



Lileraiure p. 253 



