VOL. 4 (1950) BODY SIZE AND TISSUE RESPIRATION 257 



small when the medium contains Mg ions and the period of observation is below 2 hours^^ 

 they may be neglected in many cases. 



B. MEASUREMENT OF Qq^ OF FIVE MAMMALIAN TISSUES 



1. Procedure 



At the start of this investigation it was decided to use medium II for the main 

 measurements in preference to medium I because the absorption of COg, permissible in 

 the case of medium II, simplifies the manometric technique. It was expected, on the 

 basis of the results of previous investigators on similar media^^' ^^, that the three media 

 would all give approximately the same Qq^ values, but later comparative measurements 

 of Qq2 in the three different salines gave consistent differences in the case of some 

 tissues, especially brain. 



The measurements of the O2 uptake were carried out on sliced material in conical 

 Warburg flasks of 20 to 26 ml capacity, provided with a centre well. The main compart- 

 ment contained 4 ml medium, the centre well 0.3 ml 2 N NaOH, the gas space Og. The 

 temperature was 40°. All measurements were done in duplicate. 



Five tissues, brain cortex, kidney cortex, liver, spleen, and lung, were examined. 

 They were removed from the fasting animal as soon as possible after death and placed 

 in ice-cold saline (medium III, in which the organic substrate solutions were replaced 

 by an equal volume 0.9% NaCl). Slices were made free-hand or by the method of 

 Deutsch^*. During the slicing operation the tissue and razor blades were bathed in the 

 modified medium III. Readings began after an equilibration period of 15 min and were 

 continued at 5 or 10 min intervals for 45 min, so that the total period of incubation was 

 60 min. Q02 was calculated from the pressure change observed during the 45 m.in period 

 of recording. 



Abattoir material was collected in Dewar vessels containing 250 ml water, 250 g ice, 

 3.5 g NaCl, 15 ml 1.15% KCl and 12 ml o.ii M CaCU. On addition of the tissue most 

 of the ice melted and the resulting solution contained Na, K, Ca and CI in approximately 

 physiological concentrations. The material usually reached the laboratory within about 

 one hour after killing. To test to what extent this treatment affected the rate of respi- 

 ration samples of guinea pig and rat tissue were sliced immediately after death and 

 another portion of the organ was subjected to storage in iced saline in the same way in 

 the abattoir material, except that the period of storage was 4 hours. The results are 

 shown in Table III. It will be seen that small losses of activity exceeding the limits of 

 error occurred in storing guinea pig liver and guinea pig lung. As the delay in the 

 examination of abattoir material was usually only one quarter of the time allowed for 

 storing in this experiment it may be assumed that the losses in activity due to storage 

 were negligible. If losses actually occurred the value given for abattoir material would 

 be too low. Prolonged storage in iced saline caused considerable losses of activit}'. In an 

 experiment in which guinea pig tissue was examined after a storage period of 24 hours 

 Q02 of brain cortex fell Z7%> of kidney cortex 11%, of liver 77 °o, of spleen 43%, and 

 of lung 29%. 



2. Qq^ in phosphate saline without calcium [medium II) 



Data obtained on 9 different mammalian species are given in Table IV. Of each 

 tissue 6 specimens were examined in the case of the rat, guinea pig, rabbit, sheep, cattle 



References p. 26^-26^. 



17 



