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 ineffectual to produce an increased flow through this organ, 

 if at 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 diminution 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 considerable amount, and later on reinjecting the blood so withdrawn.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 pressure is raised by reinjecting the blood which had been withdrawn.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 1 ligatured both carotids, both femorals, and 

 both ascending cervical arteries, the urine was increased from 87 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 diminished, 

 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 the cord. 1 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, N. F., Bd. iv. S. 86 (quoted by Heidenhain). 



