EXPERL \fENTS 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.e. 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 fimctions of the glomeruli and convoluted tubules, it 
would be necessary to separate in some maimer 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 How 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 woidd 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 Xussbaum's ex- 
1 Arch./, d. rjes. Physiol., Bonn, 1878, Bd. xvii. S. 580. 
