viii THE EXCRETION OF UBINE 441 



limbs of Henle's loops, and Bellini's straight tubules, he 

 attempted in the rabbit's kidney (which is the most suitable 

 because the renal medulla is not divided into pyramids) to cut out 

 the medullary substance as far as possible, in order to obtain 

 secretion from the cortical part alone, in the glomeruli and 

 convoluted tubules. 



After longitudinally dividing one of the kidneys, scooping out 

 its medulla, and then suturing and replacing the kidney, he 

 excised the kidney of the opposite side. Babbits thus operated on 

 survived only 3-4 days. On the second day the urine no longer 

 contained blood, and was less highly coloured and much more dilute 

 than normal urine. He held that this confirmed Tick's hypothesis ; 

 but in reality the greater dilution of the urine (the only result 

 arrived at) was obtained under conditions so far removed from the 

 physiological, that we fail to see how any deh'nite conclusion can 

 be deduced from it, the more so as the urine must necessarily be 

 mixed with lymph. 



Bradford's results on dogs (1892) have more weight. He 

 observed that after the extirpation of one whole and the half of 

 another kidney (so that not more than a quarter of the weight of 

 the total kidney substance was left in situ) the animal may live a 

 long time, but suffers from hydruria, i.e. it eliminates a much 

 larger volume of a urine far more dilute than normal urine, but 

 having almost the same total content of urea. 



This result resembles that of Bibbert. The hydruria may be 

 interpreted as the effect of the larger quantity of blood circulated 

 through the remaining bit of the kidney, by which compensation 

 is effected, and exaggerated filtration through the glomeruli takes 

 place. But the function of the lost tubules could only be in- 

 adequately compensated or replaced by the few tubules left, 

 whether their function be one of external, or of internal secretion. 

 In the first case the percentage of urea in the urine would be 

 diminished by the insufficient excretion of urea by the tubules, in 

 the second by the insufficient absorption of water. 



The same ambiguous interpretation attaches to the more recent 

 experiments of T. Schilling (1904), under Gerhardt's direction, in 

 rabbits that had undergone unilateral nephrectomy. He found 

 that these animals, when not hindered in drinking freely, are 

 capable of eliminating sodium chloride solutions administered by 

 the mouth as rapidly as normal animals. If, on the other hand, the 

 water supply is limited, the salt is excreted at a lower concentra- 

 tion and more slowly than in the control animal under the same 

 conditions. But when compensatory hypertrophy is complete, the 

 one kidney is capable of eliminating salt under these circumstances 

 as if the conditions were normal. On the ground of these experi- 

 ments Schilling holds it probable that the single kidney, previous to 

 compensatory hypertrophy, is only partially capable of reabsorbing 



