440 PHYSIOLOGY CHAP. 



of the renal artery from which the afferent vessels to the glomerular 

 tufts are given off, and that of the so-called renal portal vein, 

 which gives rise to the capillaries that ramify between the 

 tubules. 



Experimenting with large frogs, Nussbaum found that the 

 secretion of urine is suspended by ligation of the renal arteries ; 

 but if urea be injected into the blood, secretion is resumed, show- 

 ing (according to this author) that urea is a diuretic, i.e. a secretory 

 stimulus which excites the activity of the epithelial cells of the 

 tubules, on which it is expelled from the blood along with a certain 

 quantity of water, independent of the function of the glomeruli. 



If a solution of peptone, egg-albumin, or sugar be injected into 

 the blood of a normal foog, the whole of these substances reappear 

 in the urine, where they can easily be demonstrated ; if the injec- 

 tions are repeated after tying the renal artery, and urea be added 

 to activate the secretion, none of these substances reappear in the 

 urine. From these results Nussbaum concluded that the function 

 of the glomeruli is to eliminate water, salts, egg-albumin, sugar, 

 and peptone, while the renal tubules have the task of eliminating 

 urea, uric acid, and the other specific constituents of urine. 



These results of Nussbaum, which seemed to have finally 

 decided the controversy in favour of Bowman and Heidenhain, 

 lost much of their value by the control experiments carried out 

 by Adarni in Heidenhain's own laboratory in 1885. He showed 

 that it was impossible in the frog to exclude the vascular circula- 

 tion of the glomeruli by simply tying the renal artery, because 

 certain branches of the ovarian artery anastomose with those of 

 the renal, so that even after tying the latter it is possible to fill 

 about half the glomeruli with red pigment on injecting carmine 

 into the aorta. 



Adami further saw that if the kidneys are removed after 

 injection of defibrinated blood through the abdominal vein of 

 these frogs, and plunged into boiling water, the presence of a clot 

 of haemoglobin can be demonstrated inside Bowman's capsule. 

 This clot consists of haemoglobin and protein, showing that the 

 injected blood must have poured through the glomeruli in con- 

 siderable quantities. Nussbaum's method is not, therefore, 

 adequate to determine the paths by which substances are excreted 

 from the kidneys. 



In dogs, too, according to Adami, after tying the renal artery 

 and injecting defibrinated blood, escape of haemoglobin from the 

 glomerulus into Bowman's capsule can be detected. 



Eibbert (1883) made another attempt to distinguish the 

 functions of the various parts of the kidneys. Starting from the 

 view put forward by Fick in his Text-book of Physiology, i.e. that 

 the urine formed by the glomeruli and convoluted tubules must 

 become condensed by reabsorption of water along the narrow 



