68 THE HUMAN MECHANISM 



thyroid leads to a very serious condition, known as Graves's 

 disease or exophthalmic goiter, just as deficiency of the secre- 

 tion leads to the entirely different disease to which we have 

 already referred. 



Thus, through the medium of the blood the chemical 

 activity of one organ may affect the life of other organs 

 favorably or unfavorably. All the cells of the body help to 

 make the blood what it is, many of them contributing to it 

 something useful or even necessary to other cells. The work 

 of the body is not merely the sum total of the work of its 

 separate cells, each working for itself alone and performing 

 a single function; between the cells an exchange of prod- 

 ucts often takes place, so that cells become both serviceable 

 to and dependent upon one another for the material needed 

 to carry out their own special chemical activities. And what 

 is true of cells is no less true of organs; these also are 

 interdependent, ministering to one another. 



