CHAPTER III. 



STRUCTURE OF THE HUMAN BODY. 



1. THE human body is composed of solids and fluids. 

 These terms, however, are merely relative. There is no 

 fluid which does not contain some solid matter in solution ; 

 and no solid however dense, which does not contain some 

 fluid. The nature of both fluids and solids is essentially the 

 same, for we see one readily passing into the other ; indeed 

 no fluid long remains a fluid, and no solid a solid ; but the 

 fluid is constantly passing into the solid, and the solid into 

 the fluid. 



. 2. The relative proportion of the fluids in the human 

 body much exceeds that of the solids, the excess being about 

 8 to 1. But the excess varies according to the age. The 

 younger the age, the greater the preponderance of the fluids. 

 As age increases, the fluids gradually diminish, till in old 

 age, they become so much lessened, that the body assumes 

 a dry, wrinkled, shriveled and stiff appearance. In this 

 manner we explain the softness and roundness of the body 

 in infancy and youth, and its hard, unequal and angular 

 surface in advanced life. 



3. The fluids, then, are very important, as they furnish 

 not only the material out of which every part of the body is 

 formed, but they also furnish the medium by which the 

 noxious and useless matter is carried out of the system. 

 Every part of the body is a laboratory in which complicated 

 and translorrhing changes are constantly going on ; the 

 fluids are the materials on which these changes are wrought, 

 and the vital forces are the agents by which they are effect- 

 ed. The fluids either contribute to form the blood, or they 



