CH. xxxvi.J THE RENAL EPITHELIUM. 541 



connected with Marey's tambour gives equally good or even better 

 results. 



It is found that the effect on the volume of the organ of 

 dividing or stimulating nerves corresponds to blood-pressure. A 

 rise of blood-pressure in the renal artery is produced by con- 

 striction of the renal arterioles ; this is accompanied by a fall of 

 pressure in the renal capillaries, and a shrinkage of the kidney. 

 Increase in the volume of the kidney is produced by the opposite 

 circumstances. 



The accompanying tracing (fig. 427) shows that in a kidney 

 curve one gets a rise of volume due to each heart beat, and larger 

 waves which accompany respiration. In many cases larger sweeping 

 waves (Traube-Hering curves) are often shown as well. If a 

 kidney curve is compared with a tracing of arterial pressure, it 

 will be seen that the rise of arterial pressure coincides with a fall 

 of the oncograph lever due to constriction of the renal vessels. 



Diuretics are drugs which produce an increased flow of urine ; 

 they act in various ways, some by increasing the general blood- 

 pressure, others by acting locally upon the kidney (increasing its 

 volume as measured by the oncometer) ; under this latter head 

 are doubtless to be included some also which act on the renal 

 epithelium rather than on the blood-vessels. 



Activity of the Renal Epithelium. 



The epithelium of the convoluted tubules has a structure 

 which suggests from its resemblance to other forms of secreting 

 epitheliums, that its function here also is secreting. This is 

 confirmed by the manner in which the blood-vessels break up into 

 capillaries around these tubules ; and is further confirmed by 

 experiments. 



lii.'i'lenhiiin has shown that if a substance (sodium sulph- 

 mdigotate), which ordinarily produces blue urine, is injected 

 into the blood (after section of the medulla oblongata, which 

 causes lowering of the blood-pressure in the renal glomeruli), 

 when the kidney is examined, the cells of the convoluted tubules 

 (and of these alone) are stained with the substance, which is also 

 found in the lumen of the tubules. This shows that the pigment 

 at any rate is eliminated by the cells of the convoluted tubules, 

 and that when by diminishing the blood-pressure, the filtration 

 of urine is stopped, the pigment remains in the convoluted tubes, 

 and is not, as would be under ordinary circumstances, swept 

 away from them by the flushing of them by the watery part 

 of urine derived from the glomeruli. It therefore is. probable 



