state constitutes diseases of exhaustion, or of indirect debility. The states of accumulation and exhaustion of the excitability, in their different degrees, constitute all the diseases to which living bodies are subject.” Here the chime runs on the word _excitability_, which is not defined. If we call this property _life_, then we are only informed, that, as life is more or less vigorous, the body enjoys a greater or smaller degree of health; which we know without any medical instructor. If, instead of the accumulation and exhaustion of excitability, we take the original doctrine of excitement and debility laid down by Dr. Brown himself, we are nothing better. The whole theory is lost for want of the definition of a single word. As long as _excitability_ remains an unknown property, we can explain nothing by it. We may indeed vary our terms. We may call it _nervous influence_ with Dr. Cullen, or _sensorial power_ with Dr. Darwin; but we shall still be as much in the dark as ever; and all that can be made out of our theories, when our language is _decyphered_, must be, that sometimes people are well, and sometimes they are sick! Dr. Rush, in his Treatise on the Proximate Cause of Fever, adopts in part Dr. Brown’s system pretty nearly as the author himself laid it down. “Fevers of all kinds (says he) are preceded by general debility. This debility is of two kinds, viz. direct and indirect. The former depends upon an abstraction of usual and natural stimuli; the latter upon an increase of natural, or upon the action of preternatural, stimuli upon the body.... Debility is always succeeded by increased excitability, or a greater aptitude to be acted upon by stimuli.... The diminution or abstraction of one stimulus is always followed by the increased action of others.” Here it is evident we are as much in want of definitions as ever. We know neither what _excitability_ is, nor what _debility_ is, and yet they are both held out as the _causes_, and _proximate_ or _immediate_ causes, too, of symptoms produced by things quite obvious to our senses. Thus cold and heat, with which we are daily conversant, are only called the _predisposing_ causes of fever; while _debility_ and _excitement_, words to which we have no meaning, are said to be the _proximate_ cause. It would certainly be better to throw away such words altogether, and say that cold, heat, &c. cause fevers, without troubling ourselves farther about the matter.