These, indeed, are extreme cases: though still such as threaten many more than they actually strike; for, though uncommon, they grow out of very common habits. But even the ordinary cases of unhealthy action in the system, are sufficient to account for perhaps three-fourths of all the disquiet and bad temper which disfigure daily life. Not one man in every ten is perfectly clear of some disorder, more or less, in the digestive system--not one man in fifty enjoys the absolutely normal state of that organ; and upon that depends the daily cheerfulness, in the first place, and through that (as well as by more direct actions) the sanity of the judgment. To speak strictly, not one man in a hundred is perfectly sane even as to his mind. For, though the greater disturbances of the mind do not take place in more than one man of each thousand,[Footnote: in several nations that has been found to be the average proportion of the insane. But this calculation has never been made to include all the slighter cases. It is not impossible that at some periods the whole human race may have been partially insane.] the slighter shades that settle on the judgment, which daily bring up thoughts such as a man would gladly banish, which force him into moods of feeling irritating at the moment, and wearing to the animal spirits,--these derangements are universal. From the greater alike and the lesser, no man can free himself but in the proportion of his available knowledge applied to his own animal system, and of the surrounding circumstances, as constantly acting on that system. Would we, then, desire that every man should interrupt his proper studies or pursuits for the sake of studying medicine? Not at all: nor is that requisite. The laws of health are as simple as the elements of arithmetic or geometry. It is required only that a man should open his eyes to perceive the three great forces which support health.