But however much health may contribute to that flow of good spirits which is so essential to our happiness, good spirits do not entirely depend upon health; for a man may be perfectly sound in his physique and still possess a melancholy temperament and be generally given up to sad thoughts.  The ultimate cause of this is undoubtedly to be found in innate, and therefore unalterable, physical constitution, especially in the more or less normal relation of a man’s sensitiveness to his muscular and vital energy.  Abnormal sensitiveness produces inequality of spirits, a predominating melancholy, with periodical fits of unrestrained liveliness.  A genius is one whose nervous power or sensitiveness is largely in excess; as Aristotle[1] has very correctly observed, Men distinguished in philosophy, politics, poetry or art appear to be all of a melancholy temperament.  This is doubtless the passage which Cicero has in his mind when he says, as he often does, Aristoteles ait omnes ingeniosos melancholicos esse.[2] Shakespeare has very neatly expressed this radical and innate diversity of temperament in those lines in The Merchant of Venice: 

[Footnote 1:  Probl. xxx., ep. 1]

[Footnote 2:  Tusc. i., 33.]

Nature has framed strange fellows in her time; Some that will evermore peep through their eyes, And laugh, like parrots at a bag-piper; And others of such vinegar aspect, That they’ll not show their teeth in way of smile, Though Nestor swear the jest be laughable.

This is the difference which Plato draws between [Greek:  eukolos] and [Greek:  dyskolos]—­the man of easy, and the man of difficult disposition—­in proof of which he refers to the varying degrees of susceptibility which different people show to pleasurable and painful impressions; so that one man will laugh at what makes another despair.  As a rule, the stronger the susceptibility to unpleasant impressions, the weaker is the susceptibility to pleasant ones, and vice versa.  If it is equally possible for an event to turn out well or ill, the [Greek:  dyskolos] will be annoyed or grieved if the issue is unfavorable, and will not rejoice, should it be happy.  On the other hand, the [Greek:  eukolos] will neither worry nor fret over an unfavorable issue, but rejoice if it turns out well.  If the one is successful in nine out of ten undertakings, he will not be pleased, but rather annoyed that one has miscarried; whilst the other, if only a single one succeeds, will manage to find consolation in the fact and remain cheerful.  But here is another instance of the truth, that hardly any evil is entirely without its compensation; for the misfortunes and sufferings which the [Greek:  auskoloi], that is, people of gloomy and anxious character, have to overcome, are, on the whole, more imaginary and therefore less real than those which befall the gay and careless; for a man who paints everything black, who constantly