266 H. A. KREBS VOL. 4 (1950) 



example, in a larger species, tissue structures accessory to the main functional cells are 

 bound to constitute a relatively larger portion of the organ than in the homologous 

 tissue of a smaller animal. Such accessory structures are, among others, blood vessels, 

 glandular ducts, connective tissues. 



Thus some changes of the Qq^ values with body size may be expected in homologous 

 tissues even if the Q02 of homologous cells is the same. In general the change will be a 

 decrease with body size because cells with lower respiration, like those of connective 

 tissue, blood vessels and ducts, are bound to became more preponderant in the larger 

 species. The changes in the Q02 with body size, seen in Tables V and VII, may in part 

 be due to this factor. 



SUMMARY 



The factors affecting the rate of respiration in isolated tissues are discussed with reference to 

 the measurement of a "standard rate" of metaboUc processes in vitro. Media for the suspension of 

 tissues are devised ; their composition is essentially based on the available analytical data for blood 

 plasma. 



Q02 of liver, brain cortex, kidney cortex, spleen, and lung was measured for 9 mammalian species 

 of different body size (mouse, rat, guinea-pig, rabbit, cat, dog, sheep, cattle, horse). Three different 

 media were used ("phosphate saline without Ca", "saline low in phosphate, bicarbonate and COj" 

 and "saline serum substitute" containing physiological concentrations of inorganic ions in addition 

 to organic substrates). Kidney cortex, spleen, and liver gave about the same Q02 values in all three 

 media. Q02 for brain cortex was for all species higher in the medium containing no Ca, the average 

 level being 37-87% higher. Q02 for liver was also higher in the absence of Ca, especially in the larger 

 species. 



Q02 values of the tissues of larger animals were in general somewhat lower than the homologous 

 values of the smaller species but no strict parallelism between Q02 values and basal heat production 

 of the intact animal was found. The Q02 values for most tissues changed much less with the body 

 weight than the rate of basal heat production. 



The absolute level of Q02 in the new media (which apart from glucose contain pyruvate, fumarate 

 and L-glutamate) was higher than the values reported in the literature for saline media. They are 

 of the same order as the highest values recorded for serum. 



The characteristic differences in the basal rate of heat production in animals of different size 

 are to be attributed mainly to variation in the Q02 of the musculature. It is suggested that the Q02 

 of tissues other than muscle is in the first place governed by the specific energy requirements of the 

 tissues, and not by the heat requirements of the whole body. 



RfiSUMfi 



Les facteurs qui influencent la vitesse de la respiration dans les tissus isol6s sont discut6s par 

 rapport aux mesures d'une "vitesse standard" des processus metaboliques in vitro. L'auteur d^crit 

 des milieux de sus{tnsion de tissus; leur composition se base essentiellement sur les donn^es analyti- 

 ques connues pour le plasma sanguin. 



Le Q02 a ^te determine pour le foie, le cortex du cerveau et du rhein, la rate et le poumon de 

 9 especes de mammiferes de taille diff6rente (souris, rat, cobaye, lapin, chat, chien, mouton, b^tail, 

 cheval). Trois milieux differents ont 6te employes, le "phosphate salin sans Ca", "la solution saline 

 faible en phosphate, bicarbonate et COg et "la solution saline, rempla9ant le serum" qui contient des 

 concentration physiologiques d'ions inorganiques en plus du substrat organique. Dans les trois 

 milieux le cortex rhenal, la rate et le foie donnerent environ les memes valeurs de Qo2- Pour le cortex 

 cervical ce facteur ^lait plus ^lev^ pour toutes les especes animales examinees dans les milieux 

 exempts de Ca. En m^yenne les valeurs ^taient de 37 a 87% superieures. Pour le foie le Q02 ^tait 

 aussi sup^rieur en absence de Ca, surtout dans les especes plus grandes. 



En g^n^ral les valeurs de Q02 ^taient plus basses pour les tissus des animaux plus grands que 

 les valeurs homologues pour les animaux plus petits. Cependant nous n'avons pas trouve un parallfe- 

 lisme stricte entre les valeurs de Q02 et la production de chaleur des animaux intacts. 



Dans les nouveaux milieux (qui, a part le glucose, contiennent du pyruvate, du fumarate et 

 du L-glutamate) le niveau absolu du Q02 ^tait plus eleve que les valeurs rapportees dans la litt^rature 

 pour une solution saline. Elles sont du meme ordre que les valeurs les plus 61evees rapportees dans la 

 litterature pour le serum. 



References p. 26^—26^. 



