WORK OF KIDNEY 157 



During rest, the bulk of the oxygen consumed goes to the 

 maintenance of the kidney cells. On the average, the kidney 

 cells use about 0-04 c.c. of oxygen per gram per minute and 

 secrete about 0-003 c.c. of urine. During a period of increased 

 activity, the oxygen absorbed may rise to 0-28 c.c. per gram of 

 kidney per minute. Each c.c. of normal urine costs about 1 -05 c.c. 

 of oxygen over and above what is required for cellular use. 



The CO 2 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. 



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 minimum work done in the formation of a litre of urine may 

 be calculated from the Hill-Donnan formula. 



Work = 



=R.T.[2 (C. jog.) + 2C 4 - ZC,,] 



where R the gas constant, T absolute temperature, 



C b ^concentration in the blood of any constituent 



a, b, c, etc. 

 and C u =its concentration in the urine. 



This, of course, would only give the minimum work of the 

 kidney, even if we knew the concentration and degree of dissoci- 

 ation of each and every urinary constituent. It may be advisable 

 to call the student's attention to the fact that the energy used in 

 effecting any change is independent of the means by which that 

 change is effected. The work done, calculated from the Hill- 

 Donnan formula, is simply the minimum necessary to cause the 

 necessary change in the molecular concentration. It is independent 

 of any process and commits one to no theory (see Chap. III.). 

 Attention to this point will prevent many a ludicrous mistake. 



Rhorer has calculated the work done by the kidney in concen- 

 trating urea and sodium chloride, and from his figures Cushny 

 considers that as the concentration of urea causes the consumption 

 of about 0-7 cals., and similarly about 0-05 cals. are used in con- 

 centrating sodium chloride (per litre of urine), it would not be an 

 overestimate to state that the production of a litre of urine entails 

 the expenditure of at least 1 -2 cals. This value, however, is but 

 a fraction of the chemical energy used as determined by the 

 oxygen consumption. We have seen above that for each volume 



