_The electro-vital fluid_, in the animal economy, is subject to the same principles of polarization as the magnetic current from the artificial machine, or the magnetism of the bar-magnet. In the material organism of man, the great nerve-centers--the brain, the spinal cord, and the ganglions--appear to act the part of fixed magnets, charged with the electro-vital fluid. Indeed, there is much reason to believe that this fluid is elaborated within these nerve-centers--more especially within the brain--from the inorganic electricity of the outer world, which is supplied through the lungs in respiration, and conducted thence to these laboratories by a remarkably interesting process--a process which I have not room here to describe, but which I have drawn out in detail in a manuscript lecture on the circulation of the blood, for my classes, and which may some day see the light. These nerve-centers, viewed as magnets of electro-vitality, require to be regarded as having each a positive nucleus in the interior, on which are ranged the negative ends of the currents which go out from this positive nucleus in every direction to the surface of the medullary organ--so radiating, as it were, from center to periphery. And the nerve-lines and ramifications which issue from these great nerve-centers are polarized evidently in the same way--the electro-vital fluid being disposed with its negative ends to the positive surfaces of the nerve-centers, and its positive or plus ends to the "vital organs," and especially to the surfaces of the organism as a whole. There are many other polarizations in the human system, subordinate to those mentioned above; but I have no room to speak of them in detail. ELECTRICAL CLASSIFICATION OF DISEASES. There are two, and only two, primary classes of disease--those in which the electro-vital force is abnormally _positive_, and those where it is preternaturally _negative_. The former class comprises every variety and phase of hypersthenia, and the latter, every sort and degree of anæsthesia, or rather, of azoödynamia. _Inflammation_ may be taken as a general representative of the positive or hypersthenic class--those forms of disease in which there is too much electro-vitality, or in which the vital force may be said to be too active. _Paralysis_ may stand as a general representative of the negative or azoödynamic class--those in which the vital action is too low or weak. PHILOSOPHY OF DISEASE AND CURE.