722 THE ANATOMICAL SEPARATION OF 



high. The only point in these experiments which concerns us 

 here is the relation between the quantity of kidney substance and 

 the changes in the blood and urine. In Bradford's experiments 

 the reduction in the number of glomeruli and tubules must have 

 been about the same ; and as the urine was similar to that 

 secreted in Ribbert's experiments, it seems likely that the change 

 in the urine observed by Ribbert was due to the reduction in 

 total kidney substance. rather than to deficiency of tubules alone. 

 The change in the character of the urine observed in these ex- 

 periments is probably to be explained in the light of Galeotti's 

 results as the effort of the reduced kidney substance to excrete 

 the maximal amount of material with a minimal expenditure of 

 energy. But they do not help us to understand the mechanism 

 by which the kidney brings about this altered secretion. 



Of all the experiments dealing with the functional separation 

 of the glomeruli and tubules, those of Nussbaum are the most 

 important ; in fact, they appeared to be the crucial experiments 

 which settled once and for all the whole question which we are 

 discussing. His method was based on the anatomical fact that 

 the amphibian kidney has a double blood supply, from the renal 

 artery and from the reno-portal vein. The renal arteries alone 

 give off the vasa afferentia to the glomeruli, from which the vasa 

 efferentia pass to the capillary network round the tubules, and 

 are there joined by the branches of the reno-portal vessel. Nuss- 

 baum satisfied himself that, when the renal arteries had been 

 ligatured, the glomeruli were completely and permanently out of 

 the circulation, and that no collateral or backward circulation 

 through the glomerular capillaries was possible. He found that 

 the effect of ligature was to prevent any spontaneous secretion 

 of urine, but that a flow of urine was set up by injecting urea. 

 From this he concluded that the tubules normally excrete urea in 

 solution. He found further that dextrose, carmine, egg albumin, 

 and peptone which pass into the urine after injection into normal 

 frogs, failed to do so in ligatured frogs, even when a flow of urine 

 had been set up by injections of urea. He concluded from these 

 experiments that the glomerulus normally passes out water, salts, 

 and dextrose, and that the tubules are definitely excretory, and 

 secrete urea and similar substances in solution. A repetition by 

 Adami of these experiments threw doubt on the accuracy of 

 their anatomical basis. He found that after ligature of the 

 renal arteries a collateral circulation was set up through the 



