15S XATUKAL THEOLOGY. 



is carried into C, the ventricle ; and from this ventricle the pulmo- 

 nary artery goes off. This great artery of the lungs is for the 

 conveyance of the blood which is returned from the body into the 

 lungs. Now the great vein A, the auricle B, the ventricle C, and 

 the pulmonary artery D D, belong to the right side of the heart ; 

 or, to take a more important distinction, they convey dark-colour- 

 ed blood, which is unfit for the uses of the system. But when 

 this blood reaches the lungs, and is exposed to the atmosphere 

 we breathe, it throws off the carbon, becomes bright in colour, 

 and is called arterial blood. It returns to the heart, not to the 

 cavities which we have enumerated, but by the veins of the lungs 

 to the other side of the heart, the left — that is, to another auricle 

 and another ventricle. From this left ventricle there ascends the 

 aorta, the great artery of the body, E E. This great vessel con- 

 veys the blood to every part that has life. From all the parts of 

 the body the blood is gathered again by the extremities of the 

 veins, and so returns to the point of the auricle from which we 

 began to trace it. This short preface may make the observations 

 of the author easily intelligible.] 



The circulation of the blood through the bodies 

 of men and quadrupeds, and the apparatus by 

 wliich it is carried on, compose a system, and tes- 

 tify a contrivance, perhaps the best understood of 

 any part of the animal frame. The lymphatic 

 system, or the nervous system, may be more sub- 

 tle and intricate — nay, it is possible that in their 

 structure they may be even more artificial than 

 the sanguiferous — but we do not know so much 

 about them. 



The utility of the circulation of the blood I as- 

 sume as an acknowledged point. One grand pur- 

 pose is plainly answered by it — the distributing to 

 every part, every extremity, every nook and corner 

 of the body, the nourishment which is received into 



