STUUCTURE OF THE HUMAN BODY. 26l 



tier, they distribute nourishment, supply perspiration, and 

 renew all the waste of the system ; and by passing through 

 glands in every part of the body, all the various animal se- 

 cretions are elaborated. In the parts where the arteries are 

 lost to the sight, the veins take their rise, and in their com- 

 mencement are also imperceptible. The blood is then of a 

 dark colour. In this discoloured state it has lost some of its 

 vital power ; but on being driven through the lungs its colour 

 is restored. All this provision, however, would not be suffi- 

 cient, for the store of blood would soon be consumed, and 

 the fabric would break down, if there was not a provision 

 for fresh supplies. And we actually fmd that on its passage 

 from the lungs to the heart the blood receives a supply of a 

 new fluid extracted from the food by myriads of fine tubes 

 which carry it to a larger one, that empties itself into a large 

 vein, and being mixed with the blood is conveyed to the 

 heart. We see, therefore, by the very imperfect survey which 

 we have been able to take of this subject, that the animal 

 man must necessarily be complex in his corporeal system, 

 and in its operations. He must have one great and general 

 system, the vascular, branching through the whole circula- 

 tion ; another, the nervous, with its appendages the organs 

 of sense, for every kind of feeling ; and a third for the ccmi- 

 nexion and union of all these parts. Besides these primary 

 and general systems, he requires others which may be more 

 local or confined. One for strength, support, and protec- 

 tion ; another for the requisite motion of the parts among 

 themselves, as well as for moving from place to place, the 

 muscular system ; another to prepare nourishment for the 

 daily recruit of the body, the digestive organs; and others 

 for the various purposes of existence. 



Questions. — 1. What are the uses of the blood ? 2. Describe the 

 circulation of the blood. 3. Describe the arteries. 4. WJiat changes 

 does the blood undergo in the course of its circulation .■* 5. How is 

 provision made for a fresh supply of blood ? [Note. That cavity of 

 the heart from which the blood is driven into the arteries is called th« 

 left ventricle ; the next is called the right auricle ; the third the right 

 ventricle ; and the fourth the left auricle. ~\ 



