CIRCULATION IN SPECIAL PARTS 247 



'The liver is so vascular and distensile that it may hold one-quarter of 

 the blood in the body. 



The hepatic branches of the portal vein are supplied by vaso- 

 constrictor fibres issuing by the anterior roots from the third to the 

 eleventh thoracic nerves. 



Vaso -constrictor nerves run to the mesenteric arteries in the 

 splanchnic nerves from the fifth downwards. They have cell stations 

 in the semilunar ganglia. The upper roots go to the duodenum and 

 jejunum, the lower to the ileum and colon. The splanchnic* also 

 contain vaso-dilator fibres. They issue especially in the eleventh to 

 the thirteenth thoracic roots. Stimulation of these nerves gives a 



FIG. 129. ABTBIAL PRESSURE (1) AND OXCOMETER TRACING (2) OF KIDNEY 

 VOLUME. (Bradford.) 



Between the points starred the tenth dorsal root was excited. The time is marked 



in seconds. 



preliminary constriction, followed by a dilatation. The usual effect, 

 therefore, on the arterial pressure, of stimulating the peripheral end 

 of the splanchnic, is a big rise followed by a fall of pressure. 



The spleen is supplied through the splanchnic nerves with con- 

 strictor and inhibitory fibres. The existence of such has been demon- 

 strated by oncometry. During digestion this organ shows rhythmic 

 phases of expansion and contraction occurring at the rate of one per 

 minute. In addition, as digestion proceeds, it gradually expands for 

 several hours, and then returns slowly to its original size. The spleen 

 therefore acts as a blood-reservoir in the portal circulation. 



The Renal Circulation. The circulation in the kidney is studied 

 with great ease by the plethysmographic method. A metal oncomcter 

 was first used for this purpose. A suitable box can be moulded with- 



