ii EXTEKNAL DIGESTIVE SECKETIONS 141 



flow of blood through the liver, so the interruption of the blood- 

 stream by ligation of the hepatic artery and portal vein arrests it 

 (Kohrig). After tying the hepatic artery alone, bile may still be 

 copiously secreted, fed from the portal blood alone (Simon, Schiff, 

 Schmulewitsch, Asp). The hepatic artery supplies the nutrient 

 vessels of the gall-bladder, bile-ducts, and interlobular branches of 

 the portal system, while it takes no direct part in the formation 

 of the intralobular network of blood capillaries. For this reason, 

 ligation of the hepatic artery gives rise after some time to the 

 formation of multiple necrotic foci in the liver, the larger of which 

 are converted into cysts, while the smaller are replaced by con- 

 nective tissue, so that hepatic cirrhosis develops (CohnKeim and 

 Litten). 



The rapid and complete occlusion of the portal vein speedily 

 produces the death of the animal, owing to stasis and excessive 

 congestion of blood throughout the portal system. But if one 

 branch alone be tied, leading to one lobe of the liver, the biliary 

 secretion may continue in that lobe, fed solely by the artery 

 (Schmulewitsch, Asp). The same is also seen when ligation is 

 gradually applied to the entire portal trunk (Ore, Osier) ; also 

 when the blood of the hepatic artery is led directly into the 

 opened portal vein (Schiff). 



When arterial pressure is lowered, either by haemorrhage, or 

 from vascular paralysis consequent on section of the cervical 

 medulla, there is diminution or arrest of the bile secretion. It 

 increases, on the contrary, after section of the splanchnic, because 

 in this case, although arterial pressure is diminished, the flow of 

 blood to the liver is increased, owing to paralytic dilatation of the 

 vessels at the roots of the portal system. By a diametrically 

 opposite effect, the bile secretion diminishes with electrical excita- 

 tion of the cord, of the splanchnics, or on strychinisation of the 

 animal (Heidenhain, I. Munk). 



Circulation in the blood-vessels of the liver can be modified, 

 not only by the effects of constriction or dilatation of the roots of 

 the portal, or by increase or decrease of aortic pressure, but also 

 by the constrictor or dilator action of the nerve fibres which 

 regulate the tone of the branches of the hepatic artery and the 

 portal vein in the liver. According to certain experiments of 

 E. Cavazzani and G-. Manca (1894-95), the vaso-constrictor fibres 

 of the branches of the portal come directly from the splanchnics 

 and the caeliac plexus, and the vaso-dilators mainly from the 

 vagi. The branches of the hepatic artery, on the contrary, receive 

 their vaso- constrictors mainly from the vagi, their vaso-dilators 

 mainly from the caeliac plexus. During asphyxia, phenomena of 

 dilatation are mainly obtained in the branches of the hepatic 

 artery, and phenomena of constriction in those of the portal vein. 

 Electrical stimulation of the vagi and branches of the caeliac 



