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 hav^ 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 difrusibility, 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 living cells. The circulatory disturbance 

 which often accompanies the injection of this substance may be almost 



1 Pautynski, Virchow's Archiv, Bd. Ixxix. S. 393 ; Henschen, Akad. Afhandlung f. 

 tnedicinska Graden, Stockholm, 1879 (quoted by Sobieranski) ; v. Sobieranski, Arch. f. 

 exper. Path. u. PharmakoL, Leipzig, 1895, Bd. xxxv. S. 144. (The two first papers are 

 the subject of a critical paper by Grutzner, Arch. f. d. ges. PhysioL, Bonn, 1881, Bd. xxiv. 

 S. 441.) 



2 Arch.f. exper. Path. u. PharmakoL, Leipzig, 1895, Bd. xxxv. S. ]44. 



