438 PHYSIOLOGY CHAP. 



immediately driven out of the intracapsular space towards the 

 tubules by the stream of water, and then deposited in the lumen 

 of the canals in a semi-crystalline form after reabsorption of 

 water. 



To clear up this difficult question Heidenhain had recourse 

 to the method of Chrzouszczewsky (1866). This consists in the 

 injection of sodium sulphindigotate (indigo -carmine) into the 

 blood, and subsequent detection of the colouring substance iu the 

 kidney, after fixing it, immediately after the animal's death, by 

 injection of absolute alcohol through the renal artery. 



Indigo-carmine, when injected into the circulation of a rabbit, 

 is only eliminated by the liver and kidneys. A few minutes 

 after injection of 5 c.c. saturated aqueous solution the urine 

 becomes blue. On killing the animal and making sections of the 

 kidneys, they are seen to be the same colour, particularly towards 

 the points of the pyramids. In order to determine which cells 

 of the kidney expelled the pigment, Heidenhain arrested renal 

 secretion by a transverse section of the cervical cord, and then 

 injected indigo-carmine, killing the animal in 10 minutes, and 

 fixing the stain by injection of alcohol. On slicing up the kidney, 

 he found that the cortical part only was stained, while the medulla 

 was quite colourless. On examining the cortex under the micrc 

 scope, he saw that the blue colour was due to granules of the 

 pigment deposited in the lumen of the tubules, and also in the 

 striated cells which line them, while the intracapsular space 

 the narrow descending parts of the loops, and the collecting 

 tubules are entirely free of pigment. 



If before injecting indigo-carmine (without inhibiting the 

 secretion by division of the cord) a circumscribed zone of the 

 kidney was treated with silver nitrate, only the outer layer of 

 the cortical part stained blue, while the rest of the kidney was 

 diffusely stained. 



From these experiments Heidenhain concluded that the seci 

 tion of indigo-carmine is due to the secretory activity of the 

 striated cells of the convoluted tubules and ascending limbs of 

 Henle's loops, and assumed further that these cells, which have 

 the power of secreting an abnormal constituent from the blood, 

 must also be conceded the property of eliminating urea and the 

 other normal constituents of urine. 



Serious objections to this conclusion were, however, raised bj 

 Pautynski, Henschen, and Sobieranski (1879, 1895, 1903). The} 

 noted that if the amount of indigo-carmine injected into tl 

 blood is in excess of that employed by Heidenhain, Bowman's 

 capsules and the glomerular epithelium also show a blue tin 

 Heidenhain's data can therefore be reconciled with Ludwig's theoi 

 by admitting that the blue pigment is excreted by the glomerul 

 in very dilute solution, which is then concentrated in the tubule 



