CIRCULATION OF THE BLOOD. 145 



tions of the circulatory apparatus after death presents facts utterly inex- 

 plicable on the doctrine of the sufficiency of the heart. I have alrtady 

 mentioned the empty state of the systemic arteries ; to this may be add- 

 ed what is often witnessed the distended condition of the pulmonary 

 artery, into which the blood has been forced by the expiring beats of the 

 right ventricle, but has been unable to get through the pulmonary capil- 

 laries because of the cessation of respiration ; but in other cases, where 

 respiration has come to an end more tranquilly or slowly, the left auricle 

 is full of blood, which must have been driven into it by the pulmonary 

 capillaries. In sudden death, as by hanging and drowning, the right 

 heart is excessively distended, as is also the pulmonary artery. 



I might proceed to add to these other facts exhibiting local variations 

 of the supply of blood in the periodicities of the system. There is a cer- 

 tain amount sent to the brain during the day, and a less during the re- 

 pose of the night ; in the muscular system, during the time of its action, 

 the quantity demanded is greater ; in its state of inactivity, less. A con- 

 stant and invariable acting machine, such as is the heart, could by no 

 possibility adjust these variable supplies. But the cases here offered are 

 more than enough, and it remains to be added that, though, not one of 

 them can be explained on the doctrine of the sufficiency of the heart, 

 there is not one which does not follow as a necessary consequence of the 

 doctrine now to be presented. 



On this view, Ae circulation is conducted in the following manner: 

 The left ventricle of the heart impels the blood into all the Ex lanationof 

 aortic branches, any backward regurgitation into the auricle the circulation 

 being prevented by the shutting of the mitral valve; the oftheblood - 

 force employed is decomposed into two portions, one part exerting an in- 

 stantaneous effect on the blood in pressing it forward, and ceasing in- 

 stantaneously, and thus giving origin to the pulse ; the second distend- 

 ing the arterial tubes, but not being lost thereby, since their elasticity 

 causes them to contract, and the semilunar valves at the origin of the 

 aorta being at this period shut, a steady, onward pressure is exerted on 

 the blood ; so the quickly-ending action of the ventricle gives origin to 

 two distinct mechanical results a sudden impact and a continuous press- 

 ure. This suffices to bring the blood to the arterial origin of the capil- 

 laries, and beyond that point the action of the heart may be considered 

 not to extend. 



The relation between the interspaces of the capillaries and the blood 

 thus introduced to them continues the current. The particular mode in 

 which this relation is manifested differs in different parts. The oxidiz- 

 ing arterial blood has a high affinity for those portions that have beqpme 

 wasted : it effects their disintegration, and then its affinity is lost. The 

 various tissues require repair ; they have an affinity for one or other of 



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