49 o EXCRETION 



By tying all the arteries going to the kidneys in frogs the circula- 

 tion through the glomeruh can be completely cut off, while ligation 

 of the renal portal vein does not affect the blood-supply of the 

 glomeruli, though markedly interfering with that of the tubules. 

 Gurwitsch has found that, after ligation of the renal portal vein of 

 one kidney in (male) frogs, the flow of urine from that kidney is 

 much diminished as compared with the other. He argues that if 

 reabsorption of dilute urine filtered through the glomeruli takes 

 place in the tubules, the opposite result ought to be obtained, since 

 the glomeruli are not affected, while any absorptive power of the 

 tubules must be crippled or abolished. 



Experiments on the Excretion of Pigments by the Kidney. In 

 connection with the second question, and also incidentally with the 

 first, the results of experiments on the distribution of pigments in 



the kidney after their injection into 

 the blood have often been appealed to. 

 Heidenhain injected indigo - carmine 

 into the blood of rabbits, and after a 

 variable time killed them, cut out the 

 kidneys, and flushed them with alcohol, 

 in which the pigment is insoluble. His 

 results were as follows: (i) When the 



Fig. 191 -Diagram of Distribu- spinal CQrd was cut before the j n j ec _ 

 tion of Pigment in Kidney after , f , , , -,, -. 



injection into Blood. The cor- tion m order to reduce the blood- 

 tex between a and b and be- pressure, the blue granules were found 



tween c and d was cauterized in the < ro dded ' epithelium of the 

 before the injection. In the , , , , , , , ,, v 



blank wedge-shaped portions, i, convoluted tubules and the ascending 

 there was no pigment, in the limb of Henle's loop, and in the lumen 

 zones shaded like 2 there was of the tubules, but nowhere else. 



some pigment, but not so much . . . , 



as in the areas shaded like 3 . Bowman s capsules contained no pig- 

 ment. The renal cortex was coloured 



blue. (2) When the spinal cord was not cut, the pigment was found 

 in the medulla and pelvis of the kidney, as well as in the cortex, 

 but always in the lumen of the tubules, and not in the epithelium, 

 except in the situations mentioned. (3) If a portion of the cortex 

 of the kidney had been cauterized with nitrate of silver before in- 

 jection of the pigment, the spinal cord being left intact, a wedge of 

 the renal substance, corresponding to this area, remained coloured 

 only in the cortex, although the rest was blue in the medulla 

 also. The ' rodded ' epithelium was filled with blue granules as 

 before (Fig. 191). 



(i) shows that the epithelium is capable of excreting some sub- 

 stances at least. (2) appears to show that when the blood-pressure 

 is normal water is poured out from some part of the tubule, and 

 washes the pigment separated by the ' rodded ' epithelium down 

 towards the papillae. (3) suggests that it is through the glomeruli 



