In a work like the present, it is obviously impossible to fence round every general proposition with the numerous limitations which an unusual combination of circumstances, or a departure from the state of health, might demand. And, even if possible, it would not be necessary, as the laws of exercise have been so fully explained in the volume alluded to, that their re-discussion here would unavoidably involve much repetition from its pages. At the same time, some warning remark may be required to prevent any risk of misconception, as it might otherwise be plausibly argued, for example, that there can be no such relation as I have alleged between waste and appetite, because a European perspiring under a tropical sun incurs great waste, and yet loses both appetite and digestive power. To render this a valid exception, it must be shewn that the European is intended by Nature to live in a tropical climate, and that the diet to which he accustoms himself is that sanctioned by experience as the best adapted for his constitution; because, if neither is the case, his condition under such influences must necessarily be more or less closely allied to the state of disease, and therefore beyond the sphere to which alone my remarks are meant to apply. But even in that instance there is less contradiction than might be imagined, for the waste of the system being chiefly fluid, excites--not appetite, but its kindred sensation--thirst, to repair the loss by an unusual demand for refreshing liquids.