414 THE ELIMINATION OF WASTE PRODUCTS. 



shown in Fig. 112) the wider variations corresponding to the Traube-Hering 

 curves ; but it will be observed that in these the kidney shrinks with the 

 rise of pressure and swells with the fall. For as we have seen ( 331) 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, arid in consequence of their constriction the kidney 

 shrinks. Similarly the relaxation of the renal vessels contributes to bring 

 about the sequent fall. 



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

 ( 157) on the local and general effects of arterial constriction and dilata- 

 tion, 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, etc., of the heart's beat, (6) 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 dilatation 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, dimin- 

 ishes the pressure in the capillaries and veins which are supplied by the 

 artery. This again must not be accompanied by a too great constriction 

 elsewhere. 



2. By a lowering of the general blood-pressure, brought about (a) by 

 diminished force, etc., of the heart's beat, (0) by a general dilatation of the 

 small arteries of the body at large, or by a dilatation of vascular areas other 

 than the area in question. 



Applying these considerations to the bloodvessels of the kidney, we 

 should expect to find the following: 



A rise in general blood-pressure, and that means a rise of pressure in the 

 abdominal aorta at the mouth of the renal artery, will cause a greater flow 

 of blood through, and so an expansion of the kidney, provided that the renal 

 arteries themselves are not unduly constricted at the same time. This is 

 well shown, as we have seen, in the curve given above, where the increase 

 of pressure due to each heart-beat, as well as that due to each respiratory 

 movement, being of central origin and not due to arterial constriction and 

 being unaccompanied by any compensating constriction of the renal artery, 

 leads to expansion of the kidney, that is, to a greater flow of blood through 

 the kidney. 



If, however, the rise of general blood-pressure be due to events which at 

 the same time cause a constriction of the renal arteries, the flow through the 

 kidney may not only not be increased, but even- be diminished ; the kidney 

 may shrink instead of expanding. Thus if dyspnoea be brought about, as 

 by stopping artificial respiration during an experiment, the kidney at once 

 shrinks ; the too venous blood stimulates the vasomotor centre, and probably 

 also by direct action on the bloodvessels leads to a general arterial constric- 

 tion and so to a rise of blood-pressure ; but the renal vessels are involved in 

 this constriction, so much so that their constricted condition more than coun- 

 terbalances the general rise of blood-pressure, and less blood flows through 



