256 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



one-half of the oncometer, and the other half is shut down upon it and tightly 

 fastened, the organ is .surrounded by oil in a box which is liquid-tight at every 

 point except one, where a tube is led off to some suitable recorder such as a 

 tambour. Under these conditions every increase in the volume of the kidney 

 will cause a proportional outflow of oil from the oncometer, which will be 

 measured by the recorder, and every diminution in volume will be accompa- 

 nied by a reverse change. At the same time the flow of urine during these 

 changes can be determined by inserting a cannula into the ureter and measur- 

 ing directly the outflow of urine. By this and other means it has been shown 

 that the kidney receives a rich supply of vaso-constrictor nerve-fibres that 

 reach it between and round the entering blood-vessels. These fibres emerge 

 from the spinal cord chiefly in the lower thoracic spinal nerves (tenth to thir- 

 teenth in the dog), pass through the sympathetic system, and reach the organ 

 as non-medu Hated fibres. Stimulation of these nerves causes a contraction of 

 the small arteries of the kidney, a shrinkage in volume of the whole organ as 

 measured by the oncometer, and a diminished secretion of urine. When, on 

 the other hand, these constrictor fibres are cut as they enter the hilus of the 

 kidney, the arteries are dilated on account of the removal of the tonic action 

 of the constrictor fibres, the organ enlarges, and a greater quantity of blood 

 passes through it, since the resistance to the blood-flow is diminished while 

 the general arterial pressure in the aorta remains practically the same. Along 

 with this greater flow of blood there is a marked increase in the secretion of urine. 

 Under normal conditions we must suppose that these fibres are brought 

 into play to a greater or less extent by reflex stimulation, and thus serve to 

 control the blood-flow through the kidney and thereby influence its functional 

 activity. It has been shown, too, that the kidney receives vaso-dilator nerve- 

 fibres, that is, fibres which when stimulated directly or reflexly cause a dilata- 

 tion of the arteries, and therefore a greater flow of blood through the organ. 

 According to Bradford, 1 these fibres emerge from the spinal cord mainly in the 

 anterior roots of the eleventh, twelfth, and thirteenth spinal nerves. Under 

 normal conditions these fibres are probably thrown into action by reflex stimula- 

 tion and lead to an increased functional activity. It will be seen, therefore, 

 that the kidneys possess a local nervous mechanism through which their 

 secretory activity may be increased or diminished by corresponding alterations 

 in the blood-supply. So far as is known, this is the only way in which the 

 secretion in the kidneys can be directly affected by the central nervous system. 

 It should be borne in mind, also, that the blood-flow through the kidneys, 

 and therefore their secretory activity, may be affected by conditions influ- 

 encing general arterial pressure. Conditions such as asphyxia, strychnin- 

 poisoning, or painful stimulation of sensorv nerves, which cause a general 

 vaso- constriction, influence the kidney in the same way, and tend, therefore, 

 to diminish the flow of blood through it; while conditions which lower 

 general arterial pressure, such as general vascular dilatation of the skin 



1 Journal of Physiology, 1889, vol. x. p. 358. 



