Lastly, Let it be considered that the proper nourishment of an animal body, from which the source and materials of all muscular motion must be derived, is probably some modification of phlogiston. Nothing will nourish that does not contain phlogiston, and probably in such a state as to be easily separated from it by the animal functions. That the source of muscular motion is phlogiston is still more probable, from the consideration of the well known effects of vinous and spirituous liquors, which consist very much of phlogiston, and which instantly brace and strengthen the whole nervous and muscular system; the phlogiston in this case being, perhaps, more easily extricated, and by a less tedious animal process, than in the usual method of extracting it from mild aliments. Since, however, the mildest aliments do the same thing more slowly and permanently, that spirituous liquors do suddenly and transiently, it seems probable that their operation is ultimately the same. This conjecture is likewise favoured by my observation, that respiration and putrefaction affect common air in the same manner, and in the same manner in which all other processes diminish air and make it noxious, and which agree in nothing but the emission of phlogiston. If this be the case, it should seem that the phlogiston which we take in with our aliment, after having discharged its proper function in the animal system (by which it probably undergoes some unknown alteration) is discharged as _effete_ by the lungs into the great common _menstruum_, the atmosphere. My conjecture suggested (whether supported or not) by these facts, is, that animals have a power of converting phlogiston, from the state in which they receive it in their nutriment, into that state in which it is called the electrical fluid; that the brain, besides its other proper uses, is the great laboratory and repository for this purpose; that by means of the nerves this great principle, thus exalted, is directed into the muscles, and forces them to act, in the same manner as they are forced into action when the electric fluid is thrown into them _ab extra_. I farther suppose, that the generality of animals have no power of throwing this generated electricity any farther than the limits of their own system; but that the _torpedo_, and animals of a similar construction, have likewise the power, by means of an additional apparatus, of throwing it farther, so as to affect other animals, and other substances at a distance from them. In this case, it should seem that the electric matter discharged from the animal system (by which it is probably more exhausted and fatigued than by ordinary muscular motion) would never return to it, at least so as to be capable of being made use of a second time, and yet if the structure of these animals be such as that the electric matter shall dart from one part of them only, while another part is left suddenly deprived of it, it may make a circuit, as in the Leyden phial.