nussbaum's experiments. 423 



some at least of these substances from the blood (Bowman, Heidenhain). The 

 watery part of the urine, containing only easily diffusible salts, as it flows along the 

 tubules from the glomeruli, extracts or washes out these substances from the 

 secretory epithelium of the convoluted tubules. 



Experiments. 1. Sulphindigotate of soda and sodium urate, when injected into 

 the blood, pass into the urine, and are found within the protoplasm of the cells of 

 the convoluted tubules [only in those parts lined by " rodded " epithelium], but not 

 in the Malpighian capsules (Heidenhain). A little later these substances are found 

 in the lumen of the urinary tubules, from which they are washed out by the watery 

 part of the urine coming from the glomeruli. If, however, two days before the 

 injection of these substances into the blood, the cortical part of the kidney contain- 

 ing the Malpighian capsules be cauterised, [e.g., by nitrate of silver], or sliced off, 

 the blue pigment remains within the convoluted tubules. It cannot be carried on- 

 ward, as the water which should carry it along has ceased to be secreted, owing to 

 the destruction of the glomeruli. This experiment also goes to show that, through 

 the glomeruli the watery part of the urine is chiefly excreted, while through the con- 

 voluted tubules the specific urinary constituents are excreted. Uric acid scdts, injected 

 into the blood, were observed by Heidenhain to be excreted by the convoluted 

 tubules. Von Wittich had previously observed that in birds, crystals of uric acid 

 were excreted by the epithelium of the convoluted tubules. [The presence of 

 crystals of uric acid in the renal epithelium was observed by Bowman, and used as an 

 argument to support his theory.] Nussbaum, in 1878, stated that urea is secreted 

 by the urinary tubules and not by the glomeruli. 



The same is true for the bile-pigments, for the iron salts of the vegetable acids when injected 

 subcutaneously, and for haemoglobin. After injection of milk into the blood- vessels, numerous 

 fatty granules occur within the epithelium of the urinary tubules ( 102). 



[Nusshaum's Experiments. In the frog and newt, the kidney is supplied with 

 blood in a manner different from that obtaining in mammals. The glomeruli are 

 supplied by branches of the renal artery. The tubules are supplied by the renal- 

 portal vein. The vein coming from the posterior extremities divides at the upper 

 end of the thigh into two branches, one of which enters the kidney, and breaks up 

 to form a capillary plexus which surrounds the uriniferous tubules, but this plexus 

 is also joined by the efferent vessels of the glomeruli. These two systems are 

 partly independent of each other. After ligaturing the renal artery, Nussbaum 

 asserted that the circulation in the glomeruli was cut off, while ligature of the renal- 

 portal vein excluded the functional activity of the tubules. By injecting a sub- 

 stance into the blood, after ligaturing either the artery or renal-portal vein, and 

 observing whether it occurs in the urine, he infers that it is given off either by the 

 glomeruli or the tubules. Sugar, peptones, and egg-albumin rapidly pass through 

 an intact kidney, but if the renal artery be tied they are not excreted. Urea 

 when injected into the circulation is excreted after the artery is tied, so that it is 

 excreted through the tubules, but at the same time it takes with it a considerable 

 quantity of water. Thus, water is excreted in two ways from the kidney, by the 

 glomeruli and also from the venous plexus around the tubules along with the urea. 

 Indigo-carmine merely passes into the tubular epithelium of the convoluted tubules, 

 but it does not cause a secretion of urine. Albumin passes through the glomeruli, 

 but only after their membranes have been altered in some way, as by clamping the 

 renal artery for a time.] 



[Adami's Experiments on the kidney of the frog tend to show that Nussbaum's conclusions 

 are not justified, for Adami found that if the renal arteries in the frog be ligatured, within a 

 few hours a collateral circulation is established, and a certain amount of blood flows through 

 the kidney. He proved this by injecting into the blood, carmine or painter's vermilion, in a 

 state of fine suspension, and after ligature of the renal arteries, he found it in many of the 

 glomeruli, while laky blood similarly injected revealed its presence as menisci of Hb in the 

 Malpighian corpuscles. Even secretion of some urine may go on after ligature of the renal 



