228 General Discussion 



Adolph : I wish the structural picture agreed so well with the physio- 

 logical response to water loading. First of all, when you take out 

 one kidney from, say, a middle-aged rat, you do not reduce the water 

 diuresis much — it is more often a reduction of 20 per cent than of 50 

 per cent. Even if you take out a kidney and a half you still have 70 

 per cent of the response, and hypertrophy does not seem to be parti- 

 cularly important in restoring the response to near 100 per cent 

 (Adolph, E. F., and Parmington, S. L. (1948) Amer. J. Physiol., 155, 

 317). Similarly in the kidney of the newborn the number of nephrons 

 available, as far as anatomical studies show, is about 50 per cent of 

 that in the adult, and yet the diuresis may only be 10 per cent of the 

 adult's. As the diuresis develops in intensity with age, it gets far 

 ahead of the development of the number of nephrons or of any other 

 structure that has been counted in the kidneys. Enzyme studies 

 have been made to try and find something that would be parallel 

 either to the water diuresis or to the clearance increase with age. The 

 clearances in the newborn kidney, as far as they have been measured, 

 also develop rather slowly, but all of them are in parallel, at least in 

 the rat. This is not necessarily true in all species, because there seems 

 to be an exception in the rabbit (Levine and Levine. (1958). Amer. 

 J. Physiol., 193, 123). However, phenol red and inulin clearances are 

 proportional to one another at every age in the rat, while there is no 

 clear parallelism between any two properties of excretion except the 

 clearances. 



Desaulles: When a heminephrectomized animal is submitted, eight 

 or ten days after operation, to a physiological saline load of about 

 20 ml. /kg., the output of urine during eight hours is much higher 

 than in an animal with two kidneys. It is not at all clear to me why 

 the output is so much higher; the dilution is greater, and less sodium 

 is given out. 



Richet: It may be dependent on the amount of solutes per nephron. 



Bull: I think Dr. Richet's suggestion is a likely one. The kidney 

 lesions in severe burns are probably due to a period of low circulatory 

 volume which damages certain nephrons in several different ways. 

 The resulting morphology may be very various but the functional 

 lesion is usually rather similar in producing an oliguria, with a failure 

 of concentration. This agrees best with the idea of fully functioning 

 surviving nephrons ; any nephrons that are damaged at all are right 

 out of the picture. This explanation also agrees with our finding that 

 in old patients there is a poorer response to water load and a slower 

 excretion of sodium. 



