246 



THE CIRCULATION OF THE BLOOD 



The question may be summarized by the statement that the regulation 

 of the flow of blood through the brain is accomplished by the interaction of 

 two factors: First, the indirect regulation of blood pressure through the 

 variations in the heart's activity, and through the general action of the 

 medullary vaso-motor apparatus producing vaso-constrictions or dilatations 

 in areas other than the brain. Second, the local and direct regulation of 

 the brain vessels through reflex action on a special local vascular center. 



The Vascular Nerves for the Thoracic Viscera. Numerous efforts 

 have been made to determine the vaso-motor nerve supply for the thoracic 

 organs, the heart and lungs. In the heart the observation is rendered com- 

 plex by the fact of the rhythmic contractions which produce mechanical 

 pressure on the coronary arteries. Martin, by direct observation through a 

 lens, and Porter, by measuring the outflow of the coronaries upon vagus 

 stimulation, came to exactly opposite views: the former that the vagus con- 

 tained vaso-dilators, the latter that it contained vaso-constrictors. Still 

 other experiments have been made to prove either constrictor or dilator 

 nerves for the coronary arteries, but the first is still undetermined. 



The lesser circulation through the lungs has also proven a difficult situa- 

 tion to interpret as regards any nervous regulation of the pulmonary arteri- 

 oles. The evidence, while not conclusive, is that the vaso-constrictor supply 

 to the lungs is from the third to the fifth thoracic nerves, but that the vaso- 

 constriction produced is slight in comparison with regions of the systemic 

 circulation. 



The Vascular Nerves for the Abdominal Viscera. The vaso-con- 

 strictors and the vaso-dilators for the organs of the abdominal cavity have 

 a broad origin in the cord, from the first dorsal to the fourth lumbar in 

 the dog and cat. The nerves pass to the organs by the splanchnic nerves, 

 and by the solar, celiac, and mesenteric ganglia. The vascular nerves for 

 the different organs may be given in tabulated form: 



Organ. 



Vascular Nerves for the Abdominal Viscera. 



Course to the organ. 



/ 



Spinal origin of the vascu- 

 lar nerves. 



5, 6, 7, 8, 9, 10, n, 12, 13 D, f Splanchnic nerves and 



i L \ solar and celiac ganglia. 



3, 4, 5, 6, 7, 8, 9, 10, n, 12, J Splanchnic nerves and 



13 D, i L | solar and celiac ganglia. 



J Splanchnic nerves and 



3, 4, 5, 6, 7 , 8, 9, 10, i iD . . | ^ and celiac gangUa> 



-.. , \ 4, 5, 6, 7, 8, 9, 10, n, 12, 13 J Splanchnic and celiac 



r T \ ganglia. 



( Inferior splanchnic and 

 inferior mesenteric 

 ganglia. 



Stomach and in- 

 testine. 



Spleen ......... 



Liver . . 



Pelvic viscera . . 



D, i, 2. 3, 4 L. 

 i, 2, 3, 4L 



