INFLUENCE OF BLOOD PRESSURE. 645 
find, coincident with the rise of general blood pressure, a marked 
shrinking of the kidney. On the other hand, a dilatation of the renal 
vessels may be ^effectual to produce an increased flow through this organ, 
if ;M the same time there is a large fall of general blood pressure due 
to dilatation in other parts of the body. We may consider, in the first 
place, experiments in which the chief change has been in general blood 
pressure. It is found that, if the aortic pressure sinks below 40 mm. Hg, 
the urinary secretion stops absolutely. So long as the aortic pressure is 
above this height, the secretion is more or less proportional to the 
pressure, and changes with the changes in this pressure. Thus, if we 
stimulate the vagus in the neck, using currents sufficiently strong to 
produce a slowing of the heart-beat and a fall of blood pressure, there is 
a shrinking of the kidney and a diminuti in in the urinary flow (Goll). 
That this diminution in the flow is directly conditioned by the change in 
blood pressure due to the cardiac inhibition, is shown by the fact that 
stimulation of the vagi below the diaphragm is without effect on the 
urine (Eckhard). 
We may also alter the aortic pressure by bleeding the animal to a 
considerable amount, and later on reinjecting the blood so withdrawn. 
It is found that after the bleeding, while the blood pressure is diminished, 
the flow of urine is also lessened, but the flow increases when the blood 
pressure is raised by reinjecting the blood which had been withdrawn. 
If the aortic pressure be raised by ligaturing a number of the larger- 
arteries, the increased flow of blood through and the increased pressure in 
the kidneys are attended with increased secretion of urine. Thus in one 
experiment in which Goll l ligatured both carotids, both femorals, and 
both ascending cervical arteries, the urine was increased from 8 - 7 grms 
in 30 minutes before the ligature, to 21-2 grms. after the ligature, while 
the pressure in the aorta was raised from 127 to 142 mm. Hg. 
Division of the spinal cord. — If the spinal cord be divided in the 
upper cervical region, the result is a great fall in general blood pressure, 
which may be as low as 30 to 40 mm. Hg. In all cases where the blood 
pressure falls below 40 mm. Hg, the flow of urine is absolutely abolished. 
Since the renal vessels, like those of all other parts of the body, are kept 
in a condition of tone by impulses descending from the vasomotor centre 
in the medulla, division of the path of these impulses must cause a 
relaxation of the renal vessels, which by itself would tend to occasion 
increased blood pressure in the glomeruli. As a result of the section, 
however, the vessels all over the body are relaxed, so that the capacity of 
the vascular system is increased and the peripheral resistance chminished, 
both factors concurring to produce the large fall of pressure observed. 
This fall of pressure is more than sufficient to counterbalance the local 
renal dilatation, so that there is diminished blood flow through the 
kidney, as is shown by the marked shrinking of the oncometric curve of 
the kidney on section of the cord. 
Stimulation of th cord} — If the peripheral end of the divided cord be 
stimulated with an induction current, universal constriction of the blood 
vessels and a large rise of blood pressure are produced. This, however, is 
incompetent to bring back the urinary flow which has been abolished by 
the previous section, since the renal vessels concur in the general con- 
striction, and the kidney shrinks still further in spite of the raised blood 
pressure. If, however, this local constriction be prevented by previous 
1 Ztschr.f. rat. Med., 1854, K ¥.. Bd. iv. S. 86 (quoted by Heidenhaiu). 
