DEFENSES OF THE BODY 137 



logical process or constituent; it appeared to many 

 as the intrusion of a wholly inexplicable and unre- 

 lated cause of disease. Philosophically-minded inves- 

 tigators had faith that in time the oxybutyric acid 

 would be found to stand in some clear relation to 

 physiological processes, and this view has been 

 amply justified by recent studies. For it has been 

 shown that this obscure acid comes from the normal 

 oxydative breakdown of fatty acids. In health 

 the acid exists hi mere traces only, because it is 

 burned to simpler substances as quickly as it is 

 formed, thus serving as a source of energy. But in 

 diabetes, the power of complete combustion is lost, 

 and a portion of the acid formed escapes unburned 

 into the urine. What seemed a new and unrelated 

 substance is, in reality, only a physiological con- 

 stituent that has been subjected to a great quanti- 

 tative change in consequence of a 'partial breakdown 

 in the oxidative mechanism. 



There has long been a disposition to make a sharp 

 distinction between structural and functional 

 diseases. It is important to realize that disease is, 

 in its essence, the expression of functional derange- 

 ment, and that disturbances of function, however 

 slight in degree, imply structural alterations of some 

 grade, even though these be undetectable by present 

 methods of investigation. The standards of judg- 

 ment in respect to structural disease vary from 

 generation to generation as methods grow more 

 refined and searching. Even to-day we have definite 



