654 THE SECRETION OF URINE. 
limb of Henle's loop, the capsules and the collecting tubules as well as 
the descending loop of Henle being quite free from pigment. 
A very interesting appearance is offered by the kidney, if, previous 
to the injection, its surface has been cauterised over a small area with 
silver nitrate, the cord being intact. In the cauterised zones, the secre- 
tion of water is stopped, but the excretion of indigo-blue is not affected, 
so that in these zones the blue colour is confined to the cortex, whereas 
in the rest of the kidney the coloration is diffuse. Heidenhain con- 
cludes from these observations that the excretion of indigo-blue is due 
to the specific secretory activity of the striated cells lining the con- 
voluted tubules and ascending loop of Henle. Since these cells are the 
only cells of the kidney which have the power of excreting indigo- 
carmine, an abnormal constituent of the blood, it is natural to assume 
that they may also possess the specific function of secreting the urea of 
normal urine. 
These conclusions of Heidenhain's have not, however, passed un- 
challenged. Various observers have pointed out that, in order to obtain 
the results described by Heidenhain, it is necessary to repeat exactly all 
the details of his experiments. If we inject larger doses of the 
sulphindigotate and kill the animal ten minutes after the injection, it 
will be found that, in addition to the staining of the striated cells of the 
convoluted tubules, and the deposition of precipitated pigment in the 
lumen of these tubules, there is also a slight staining of Bowman's 
capsule and the glomerular epithelium. It has been suggested 1 that 
Heidenhain's results might be equally well explained on Ludwig's 
hypothesis, according to which a dilute solution of the dye would be 
exuded into Bowman's capsules, and would be concentrated by absorption 
of fluid on its way through the convoluted tubules. Indigo-carmine is 
soluble in water and in very weak salt solution, from which it is 
precipitated on concentration. Moreover, indigo-carmine is liable to 
reduction in the living tissues with the formation of a colourless 
product, and these two factors, i.e. reduction of the pigment and the ex- 
treme dilution of the glomerular exudation, have been held to explain 
the absence of glomerular staining in Heidenhain's experiment. By 
increasing the dose injected into the veins and killing the animal soon 
after the injection, these two factors are minimised and a staining of the 
capsules is brought about. Sobieranski 2 points out that the staining or 
deposition of granules in the cells of the convoluted tubules is confined 
to the parts of these cells bordering on the lumen — a fact which seems 
to indicate that the pigment has been taken up by these cells from the 
lumen rather than from the surrounding lymph spaces. 
These observations are to a certain extent confirmed by the effects of 
the injection of carmine. This substance, which has a much more com- 
plicated composition than sodium sulphindigotate, enjoys the correspond- 
ing advantage of smaller diffusibility, so that it can be more easily traced 
on its way through the tissues of the body. Moreover, it undergoes no 
reduction in contact with the bving cells. The circulatory disturbance 
which often accompanies the injection of this substance may be almost 
1 Pautynski, Virchoxo's Archiv, Bd. lxxix. S. 393 ; Henschen, Akad. Afhandlwng /'. 
medicinska Graden, Stockholm, 1879 (quoted by Sobieranski) ; v. Sobieranski, Arch. f. 
exper. Path. u. Pharmakol., Leipzig, 1S95, Bd. xxxv. S. 144. (The two first papers are 
the subject of a critical paper by Griitzner, Arch. f. d. gcs. Physiol., Bonn, 1881, Bd. xxiv. 
S. 441.) 
2 Arch. f. exper. Path. u. Pharmakol,, Leipzig, 1895, Bd. xxxv. S. 144. 
