196 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



blood sent out of the left heart in a minute may pass through the kidneys, 

 although the combined weight of these organs makes only 0.56 per cent, of 

 that of the body. 



The richness of the supply of vaso-motor nerves to the kidney and the con- 

 ditions which bring them into activity are fairly well known, owing to the use- 

 ful invention of the oncometer by Roy. 1 This instrument is in principle a 

 plethysmograph especially modified for use upon the kidney of the living 

 animal. It is a kidney-shaped box of thin brass made in two parts, hinged at 

 the back, and with a clasp in front to hold them together. In the interior of 

 the box thin peritoneal membrane is so fastened to each half that a layer of olive 

 oil may be placed between it and the brass walls. There is thus formed in 

 each half a soft pad of oil upon which the kidney rests. When the kidney, 

 freed as far as possible from fat and surrounding connective tissue, but with 

 the blood-vessels and nerves entering at the hilus entirely uninjured, is laid in 

 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 which 

 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-medullated 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, 2 these fibres emerge from the spinal cord mainly in the 



1 See Cohnheim and Roy : Virchow's Archiv, 1883, Bd. 92, S. 424. 



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



