158 PHYSFOLOGY. 



( 

 SECT. III. 



OF THE CIRCULATION OF THE BLOOD. 



CXLVI. The circulation of the blood, by CXXIX., seems 

 necessary to the excitement of the brain ; and for this, as well 

 as other reasons, it is, next after the function of the brain itself, 

 the most important of the animal economy. 



On this subject we shall consider, 1. The course of the blood, 

 2. The powers by which the blood is moved. 3. The laws and 

 general circumstances of the circulation. 4. Respiration as ne- 

 cessary to it. 



On all these subjects we suppose the anatomy of the parts 

 to be known. 



CHAP. I. OF THE COURSE OF THE BLOOD. 



CXLVI I. Wounds and haemorrhagies shew that, in living 

 bodies, the blood is in constant motion, and flowing into one 

 part from many others. 



CXLVIII. In man, and other analogous animals which have 

 once breathed for some time, the course of the blood is very con- 

 stantly in the following manner. 



From the left ventricle of the heart, the blood passes into the 

 trunk of the aorta, and successively into the following vessels 

 and cavities, viz. The branches of the aorta, the branches of the 

 vena cava, the trunk of the same, the right auricle of the 

 heart, the right ventricle of the same, the pulmonary artery, 

 the pulmonary veins, the left auricle of the heart ; from which 

 last it passes into the left ventricle of the heart to return again 

 into the same course as before. 



From all this, it appears that in the arteries the usual course 

 of the blood is from the heart towards the extreme branches of 

 these ; and that in the veins the course is in the contrary di- 

 rection, from the extreme branches towards the heart. 



CXLIX. The course of the blood through the cavities of 

 the heart, as above described, is not in a continued stream, but 

 alternately interrupted and free during the contraction and di- 



