THE LIVING ORGANISM 201 



strable to the unaided eye, and in other cases 

 only when the aid of the microscope is 

 invoked, passes even beyond visible structure, 

 onward into the region of chemical structure, 

 for it is found that nearly every tissue (or 

 assemblage of similar cells) of the body 

 secretes certain chemical substances into the 

 general blood stream which are carried around 

 to another situation in the body where there 

 is a different assemblage of another kind of 

 cell to be benefited by this internal secretion, 

 as it is called. So close is this chemical 

 sympathy, and so absolutely necessary are 

 the chemical substances so formed, which 

 have been called hormones, or excitants, that 

 the loss of one of them in many well-known 

 instances leads to such changes that the 

 death of the whole animal results. 



This kind of biological civilization, or 

 social economy, within the whole animal, 

 and the interdependence of all parts upon 

 a wide commerce of exchange, is the most 

 fundamental thing in the physiology of the 

 higher animal. Apart from gross lesions 

 due to injury, it may be said that all the 

 problems of disease, and all the causes of 

 death, depend upon the upset of the delicate 

 balance of such chemical exchanges between 

 the various types of cells composing the body. 



