260 STRUCTURE OF THE HUMAN BODY. 



LESSON 118. 



Structure of the Human Body (continued.) 



Socre'tion, the process by which various fluids are separate 

 from the blood by means of the glands. Vas'cular, full of ves- 

 sels. 



The mind being formed for society and intercourse with 

 beings of her own kind, she must be endued with powers of 

 expressing and communicating her thoughts by some sensi- 

 ble marks or signs, which sh;ill be both easy to herself, and 

 admit of great variety ; and accordingly she is provided with 

 the organs and the faculty of speech, by which she can throw 

 out signs with amazing facility, and vary them without end. 

 Thus we have built up an animal body which would seem 

 to be pretty complete ; but as it is the nature of matter to be 

 altered and worked upon by matter, so in a little time such 

 a living creature must be destroyed, if there is no provision 

 for repairing the injuries which she must commit on her- 

 self, and those to which she must be exposed from without. 

 Therefore a treasure of blood is actually provided in the 

 heart and vascular system, full of nutritious and healing par- 

 ticles, fluid enough to penetrate into the minutest parts of 

 the animal ; impelled by the heart, and conveyed by the ar- 

 teries, it pervades every part, builds up what was broken 

 down, and sweeps away the old and useless materials. Hence 

 we see the necessity or advantage of the heart and arterial 

 system. The heart consists of four cavities, from one of 

 which, the blood is driven into the arteries through the body, 

 by another, it is received back again by the veins : it then 

 passes into the third, whence it is forced into the lungs. 

 Having there been revivified by coming in contact with the 

 air, it is carried back by a set of veins into the fourth cavity, 

 and thence into that in which it began its course : it is then 

 again forced into the arteries, brought back by the veins, 

 and thus circulates till the end of life. Each cavity of the 

 heart is generally called into action four thousand times 

 every hour. The arteries, into which the blood is forced, 

 branch in every direction through the body, like the roots, 

 branches, and leaves of a tree, running through the substance 

 fif the bones, and every part of the animal, till they are lost 

 in such fine tubes as to be wholly invisible. In this man- 



