528 FLOW OF BLOOD THROUGH KIDNEY. [Book n. 



swells with the fall. For as we have seen (§ 315) the rise in 

 the Traube-Hering undulation is due to an augmentation of 

 peripheral resistance caused by the constriction of minute arte- 

 ries ; and this constriction occurs in the kidney as elsewhere ; 

 the renal arterioles take their share in producing the result, 



BLOOD 



PRESSURE 



KIDNEY CURVE 



Fig. 104. Blood-presstjre tracing, and Curve from Renal Oncometer. 

 Natural size. The blood-pressure abscissa line has been raised 2-75 cm. (the 

 actual medium blood-pressure having been 115 mm. Hg.). The 'time-curve gives 

 interruptions recurring every three seconds. 



and in consequence of their constriction the kidney shrinks. 

 Similarly the relaxation of the renal vessels contributes to 

 bring about the sequent fall. 



§ 331. In the course of a discussion in an earlier part of 

 this work (§ 149) on the local and general effects of arterial 

 constriction and dilation, we saw that the local blood-pressure 

 in and flow of blood through the capillaries and other minute 

 vessels of this or that vascular area may be increased — 



1. By an increase of the general blood-pressure, brought 

 about — (a) by an increased force, frequency, &c. of the heart's 

 beat, (ft) by the constriction of the small arteries supplying 

 areas other than the area in question. 



2. By a relaxation of the artery (or arteries) supplying 

 the area itself, which, while diminishing the pressure in the 

 artery itself, increases the pressure in the capillaries and small 

 veins which the artery supplies. It need hardly be added that 

 this local relaxation must not be accompanied by a too great 

 dilation elsewhere. 



The same local blood-pressure and flow of blood may simi- 

 larly be diminished — 



1. By a constriction of the artery of the area itself (and 

 its branches), which, while increasing the pressure on the 

 cardiac side of the artery, diminishes the pressure in the capil- 

 laries and veins which are supplied by the artery. This again 

 must not be accompanied by a too great constriction elsewhere. 



