248 A TEXTBOOK OF PHYSIOLOGY 



out difficulty out of gutta-percha (Fig. 120). The kidney, having been, 

 exposed by a lumbar incision, is drawn out of the wound and placed 

 in the box. The pedicle of the kidney passes out through a groove 

 in one side of the chamber. The box is closed by a glass cover, and 

 this is made air-tight by a free application of thick vaseline. The altera- 

 tions in the volume of the kidney are recorded by means of a tambour. 

 The tracing of renal volume follows exactly the curve of arterial pres- 

 sure, and exhibits both the cardiac and respiratory oscillations. 



Excitation of the splanchnic nerves produces constriction of the 

 kidney. The renal vaso -motor fibres to the anterior roots arise from 

 the sixth to the thirteenth thoracic nerves. Most of the renal vaso- 

 niotor fibres are found in the eleventh, twelfth, and thirteenth 

 nerves. 



By reflex excitation it is more common to obtain contraction than 

 expansion of the kidney, but expansion is frequently witnessed when 

 the central ends of the eleventh, twelfth, and thirteenth posterior 

 thoracic roots are stimulated. Vaso-dilator fibres in the anterior 

 roots are evidenced by employing a slow rate of excitation (one per 

 second). 



Injections of normal saline, or of a 2 to 3 per cent, solution of 

 caffeine of soda, double the velocity of blood-flow in the renal artery, 

 as measured by the stromuhr. This occurs after section of the renal 

 nerves. Hence the diuretic action of these drugs. 'If urea be in- 

 jected, it produces local dilatation of the kidney, while it excites the 

 vaso-motor centre and causes general vaso -constriction. 



The Circulation in the Generative Organs. Excitation of the first 

 and second sacral nerves in the dog produces erection of the penis. 

 The existence has been demonstrated of a centre in the lumbar region 

 of the cord, by means of which erection can be reflexly excited. In 

 the rabbit, monkey, and cat, the vaso-dilators run in the second and 

 third anterior sacral roots. 



The outflow from the vena pudenda communis is increased as much 

 as eight times on excitation of the nervi erigentes. The vaso -con- 

 strictor fibres issue from the third, fourth, and fifth lumbar anterior 

 roots. 



The internal generative organs are supplied with vaso -constrictor- 

 nerves from the lumbar anterior roots. 



All the vaso-constrictor fibres to the generative organs pass through 

 cells stationed in the inferior mesenteric and sacral ganglia of the 

 sympathetic. The vaso -dilator nerves pass through cell stations in 

 scattered ganglia situated near these organs. 



The Foetal Circulation. In the mature foetus, the fluid brought 

 from the placenta by the foetal umbilical vein is partly conveyed at 

 once to the vena cava ascendens by means of the ductus venosus. 

 and partly flows through two trunks that unite with the portal vein, 

 returning the blood from the intestines into the substance of the liver, 

 thence to be carried back to the vena cava by the hepatic vein. Having 

 thus been transmitted through the placenta and the liver, the blood 



