198 THE ARMY FOR HOME DEFENCE 



sulphate must have been added to the Ihiid during its stay in the 

 tubule or chloride and water absorbed from it. The two main 

 modern theories of renal action differ on this point. The experi- 

 ment is quoted at this stage to demonstrate that it is probable that 

 sulphate stinuilates the cells lining the tubule, and that their 

 activity entails the consumption of oxygen and the expenditure 

 of energy. 



Energy Used. The consumption of oxygen, as we have seen, is 

 an indication of energy usage, and the amount of oxygen used 

 gives a measure of the amount of energy used. Assuming that 

 the oxygen all goes to the oxidation of glucose, then- each cubic 

 centimetre of oxygen will cause the liberation of 0-005 Cal. 

 from 1-5 mgrms. of glucose. 



Basal Metabolism of Kidney. When the kidney is at rest, that 

 is, when minimal amounts of urine are being formed, very little 

 work beyond the domestic upkeep of the kidney cells is being 

 performed and very little oxygen is consumed. A kidney in this 

 condition, forming 0-03 c.cm. of urine per minute, used 0-4 c.cm. of 

 oxygen corresponding to the evolution of 0-002 Cal. from the 

 oxidation of 0-6 mgrm. of glucose. 



Metabolism by Secreting Kidney. During the secretion of 2 c.cms. 

 of urine per minute the kidney consumes about 2-4 c.cm. of oxygen. 

 Subtract from this amount the amount of oxygen necessary for the 

 upkeep of the cells (basal rate 0-4 c.cm. per minute) and you have 

 the amount of oxygen used in the formation of 2 c.cms. of urine. 

 That is, each litre of urine formed entails the consumption of about 

 an equal volume of oxygen and 1-3 grams of glucose (approx.) with 

 an energy utilisation of 5 Cals. 



The COo output varies very much even during rest and does not 

 always increase in proportion to the oxygen absorbed. It may 

 be that this metabolite is excreted by some other channel than the 

 blood stream. 



Work Done by Kidney. Attempts have been made to correlate 

 the total energy exchange in the kidney with the work done, 

 calculated from the alteration in the osmotic concentration in the 

 various urinary constituents. The mininuun work done in the 

 formation of a litre of urine may be calculated from the Hill-Donnan 

 formula : — 



Work = R.T. ^e{c„ log, ^^^ + ZC, - ZC^ 



where R = the gas constant, T = absolute temperature, 



C^, = concentration in the blood of any constituent 

 a, b, c, etc. 

 and C„ = its concentration in the urine. 



