164 THE MECHANISM OF THE CIRCULATION. 



traced the efferent fibres to the semilunar ganglion and to the greater 

 splanchnic nerve of the left side only. Thence he traced them to the 

 anterior roots of the thoracic nerves on the left side from the third to 

 the tenth. Schafer and Moore have shown, however, that contraction of 

 the spleen is obtained on stimulating either splanchnic nerve. 1 They 

 determined the outflow of splenic fibres to arise from the anterior roots 

 of both sides, from the third to the fourteenth post-cervical nerves. The 

 largest effect was obtained by excitation of the sixth, seventh, and eighth 

 roots. Each left root produced a relatively greater contraction than the 

 corresponding right one. They were unable to confirm Bulgak's obser- 

 vations as to the afferent fibres of the organ. 



In one case dilatation of the spleen was obtained by weak excitation 

 of the splanchnic nerve, and constriction by strong excitation, and hence 

 they conclude that this nerve contains both constrictor and dilator fibres. 



They further found, in opposition to Boy, that excitation of the 

 peripheral end of the thoracic or of the atropinised cervical vagus 

 produces no effect on the spleen. There appeared to be no means of 

 separating the vasomotor effects on the splenic vessels from the con- 

 tractility of the muscular tissue of the spleen itself. Apparently the 

 whole organ acts in the same manner as the muscular wall of the 

 arterioles, and thus the organ controls its own blood supply. 



THE PANCREATIC CIRCULATION. 



After tying some of the branches of the arteria pancreatico-duodenalis, 

 Franqois-Franck and Hallion 2 placed the pancreas in a plethysmograph 

 of suitable shape. They obtained evidence of vaso-constricton on excita- 

 tion of the splanchnic nerves on either side, and traced the origin of the 

 constrictor fibres to the anterior roots from the fifth thoracic to the 

 first lumbar nerves. Expansion of the pancreas seemed to follow 

 excitation of the peripheral end of the vagus. Eeflex constriction of the 

 organ was produced by stimulation of any sensory nerve, or of the 

 cerebral cortex ; reflex dilatation, by excitation of the central end of 

 the vagus. During the first stage of an asphyxial rise of blood pressure 

 the pancreas is contracted in volume. 



THE CORONARY CIRCULATION. 



In the dog, the left coronary artery supplies the left ventricle and 

 intraventricular septum. From thence arise the ramus descendens and 

 the ramus circumflexus. The ramus descendens passes down the intra- 

 ventricular groove, and gives off the septal branch ; the ramus circum- 

 flexus passes to the left along the auriculo-ventricular groove. The 

 right coronary artery supplies the right ventricle and auricle ; it is 

 much smaller than either branch of the left coronary artery. The 

 branches of these arteries are physiologically, but not anatomically, 

 terminal. The resistance in the narrow communicating branches is 

 too great for an efficient circulation to be maintained through them. 

 Thus, closure of any one of them is followed by sudden anaemia and 

 infarction of the capillary areas which they supply. That the part of 

 the heart wall supplied by the infarcted artery degenerates, has experi- 

 mentally been determined in the dog. 



1 Loc. cit.\ cf. Schiff, " Lecons surla physiol. de la digestion, " Paris, 1867, tome ii. p. 451. 



2 Compt. rend. Soc. de biol., Paris, 1896, p. 561. 



