EXPERIMENTS OF NUSSBA UM. 65 5 



entirely avoided by using a solution of carmine in very weak soda, and 

 carrying out the injection slowly (10 c.c. in five minutes). If we kill 

 the animal thirty to forty minutes after the injection, and wash out the 

 kidney from the renal artery with absolute alcohol, we find the glomeruli 

 stained, the nuclei being red, the glomeruli themselves being of a fainter 

 reddish tinge. The epithelium of the convoluted tubules contains fine 

 granules of pigment towards the inner part of the cells, and here and 

 there deposits of carmine are seen in the straight tubules. Under no 

 circumstances are the pigment granules ever found in the basal parts of 

 the epithelial cells. There can be no doubt that these appearances 

 suggest that the pigment has been taken up by the cells from the lumen 

 rather than that it is in the act of excretion by the cells. In neither of 

 these two experiments do the facts at our command allow us to come to 

 a definite conclusion with regard to their interpretation. In order to 

 decide the relative functions of the glomeruli and convoluted tubules, it 

 would be necessary to separate in some manner the activities of these 

 two parts of the kidney, so as to obtain the action of one or other of 

 them in an isolated form. 



Experiments of Nussbaum. A method for attaining this object 

 was devised by Nussbaum, 1 and promised at first to be of crucial 

 importance for the physiology of urinary secretion. The kidneys of 

 amphibians possess, as Bowman pointed out, a double vascular supply, 

 i.e. from the renal artery and from the renal portal vein. From the 

 former vessel are derived the vasa afferentia to the glomeruli, whereas 

 the latter breaks up into capillaries which anastomose round the 

 tubules, in conjunction with the capillary ramifications of the efferent 

 vessels of the glomeruli. Nussbaum imagined, therefore, that the 

 glomerular activities might be altogether excluded by ligature of 

 the renal artery. Carrying out a number of experiments of this 

 description, he obtained results which seemed to decide absolutely in 

 favour of Heidenhain's hypothesis. Thus, after ligature of the renal 

 arteries in frogs, the urinary flow was abolished. A flow of urine 

 might, however, be evoked by the injection of urea into the blood, 

 proving, according to Nussbaum, that the substance was not excreted 

 by the glomeruli but by the tubules, and also that the latter struc- 

 tures could, under the influence of diuretics, secrete part of the water 

 of the urine. In a normal frog the injection of peptone, egg-albumin, 

 or sugar into the blood is followed by the excretion of these substances 

 in the urine. If, however, the renal arteries be previously tied, none 

 of these substances appear in the urine, even when a urinary flow is 

 produced by the injection of urea. Carmine also, which is acknow- 

 ledged by all observers to be excreted by the glomeruli, does not 

 appear in the urine of the frog, if the renal arteries be ligatured. 

 Nussbaum concluded, therefore, that the excretory apparatus of the 

 kidney consisted of two parts, namely, the glomeruli, which excreted 

 water and salts as well as egg-albumin, peptone, and grape-sugar ; and 

 the tubules, which excrete urea and probably uric acid, together with 

 a certain proportion of water. 



These experiments are so definite that they would seem to decide 

 the question as to the part played by the various structures of the 

 kidney, were it only possible to place reliance on them. This un- 

 fortunately is not the case. A careful repetition of Nussbaum's ex- 



1 Arch.f. d. ges. PhysioL, Bonn, 1878, Bd. xvii. S. 580. 



