CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 



691 



these the kidney shrinks with the rise of pressure and swells with 

 the fall (Fig. 90 does not shew these wider variations). For as 



BLOOD PRESSURE 



KIDNEY CURVE 



FIG. 90. BLOOD-PRESSURE TRACING, AND CURVE FROM KENAL 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. 



we have seen ( 388) the rise in the Traube-Hering undulation 

 is due to an augmentation of peripheral resistance caused by the 

 constriction of minute arteries; and this constriction occurs in 

 the kidney as elsewhere ; the renal arterioles take their share in 

 producing the result, and in consequence of their constriction the 

 kidney shrinks. Similarly the relaxation of the renal vessels 

 contributes to bring about the sequent fall. 



411. In the course of a discussion in an earlier part of this 

 work ( 171) 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, (b) 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 similarly 

 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 capillaries and veins 



