ABSTRACT
The change that accompanies the exercise of function may be chemical, morphologic, or physical; as a rule it partakes of all the qualities in varying degree. The changes, chemical and morphologic, taking place in muscles and nerve-cells during the exercise of function indicate a consumption of tissue—a consumption which depends directly upon increased oxidation. Excessive exercise of function, leads primarily to the excessive consumption of tissue. Under these circumstances the waste substances thrown into the circulation are present in abnormal amount, and instead of a sedative or retarding influence, exert a toxic action. They no longer act as gentle restrainers of function, as preventives of unphysiologic waste, but as poisons. Persistent excess of function leads inevitably to morbid organic changes. These changes result from two causes: first, the direct effect of the excessive function upon the organ concerned; and, second, the toxic action of waste substances present in abnormal amount or changed in character.
