CH. XXXVI.] ACTIVITY OF THE RENAL EPITHELIUM 547 



cells and convoluted tubes much in the same way as Heidenhain's 

 blue pigment. 



Other experiments, however, have been undertaken to prove the 

 point for the case of urea. 



If the part of the cortex of the kidney which contains the 

 glomeruli is removed, urea still continues to be formed. This is a 

 proof that the excretion is performed by the portions of the con- 

 voluted tubules that remain, 



By using the kidney of the frog or newt, which has two distinct 

 vascular supplies, one from the renal artery to the glomeruli, and the 

 other from the renal-portal vein to the convoluted tubes, Nussbaum 

 stated that certain foreign substances, e.g. peptones and sugar, when 

 injected into the blood, are eliminated by the glomeruli, and so are 

 not got rid of when the renal arteries are tied ; whereas certain other 

 substances, e.g. urea, when injected into the blood, are eliminated by 

 the convoluted tubes, even when the renal arteries have been tied. 

 These experiments have, however, been subjected to considerable 

 criticism, and some observers have failed to obtain the same result. 

 A re-investigation of the subject has been recently undertaken by 

 Dr A. P. Beddard. He finds that ligature of all the arteries to the 

 kidneys in the frog cuts the glomeruli completely out of the circula- 

 tion. Adami's failure to confirm Nussbaum was due, not as he 

 supposed to anastomoses between the terminations of the renal artery 

 and the renal-portal system, but to incomplete ligature of the 

 arteries. When the glomeruli are shut off in this way, no secretion 

 takes place either spontaneously or after injection of urea, which is 

 a diuretic ; the contrary results obtained by Nussbaum were due to 

 imperfect ligature, so that a number of glomeruli were left intact. 

 Nussbaum's anatomical facts were therefore right, but his physio- 

 logical experiments were faulty. A certain supply of arterial blood 

 is necessary to the normal life of the renal epithelium, for this 

 undergoes fatty degeneration and comes away (desquamates) in con- 

 sequence of the occlusion of the glomeruli. Beddard's experiments, 

 though important, do not really settle the question concerning the 

 normal function of the epithelium of the tubules ; they suggest that 

 another series of experiments must be undertaken, in which an 

 adequate supply of oxygen to the epithelium is ensured after com- 

 plete ligature of all the arteries. 



The Work done by the Kidney. 



We have already seen (p. 321) the great importance a study of osmosis in the 

 body has in the understanding of many physiological facts. 



The urine is separated from the blood by a process which is not simply 

 filtration, and if we measure the work of the kidney it is found to be vastly greater 

 than could be produced by the intra-capillary blood-pressure. Ludwig held that 

 re-absorption of some of the water and salts which escape at the glomeruli takes 



