4 THE HUMAN BODY. 



These fluids are classed, according to the part they play in 

 the human economy, into constituent fluids, secreted fluids 

 or secretions, excretions, and intermediate products, which 

 partake of the nature of the other three. The constituent 

 fluids are three in number the blood, chyle, and lymph. 

 The blood is the nutritive fluid of the body; it contains all 

 the immediate principles that are found in its organism. In- 

 cessantly renewed by digestion and respiration, it supplies 

 to each organ assimilable matter, and to the special labora- 

 tories the materials for the secretions, and carries off the 

 results of disassimilation which are to be thrown out of the 

 organism. It is therefore at once a reparative and a purify- 

 ing fluid. The term " fluid flesh," which has been applied 



Fig. i. Blood seen under the microscope. 



to it, is incomplete, for it contains not only the muscular 

 tissue, but the essential elements of all the other tissues are 

 found in its mass. 



The blood is heavier than water, its specific gravity being 

 1052 to 1057, while that of water is 1000. In the blood- 

 vessels the blood is composed of ist. anatomical elements, 

 red and white corpuscles. 2d. Of a fluid, of which 779 parts 

 in weight in 1000 are water in men, and in women 791 

 parts in 1000. This fluid is the plasma, the plastic substance, 

 the nourishing juice in which are found all the immediate 



