Be very careful to whom you trust one of these keys of the side-door.  The fact of possessing one renders those even who are dear to you very terrible at times.  You can keep the world out from your front-door, or receive visitors only when you are ready for them; but those of your own flesh and blood, or of certain grades of intimacy, can come in at the side-door, if they will, at any hour and in any mood.  Some of them have a scale of your whole nervous system, and can play all the gamut of your sensibilities in semitones,—­touching the naked nerve-pulps as a pianist strikes the keys of his instrument.  I am satisfied that there are as great masters of this nerve-playing as Vieuxtemps or Thalberg in their lines of performance.  Married life is the school in which the most accomplished artists in this department are found.  A delicate woman is the best instrument; she has such a magnificent compass of sensibilities!  From the deep inward moan which follows pressure on the great nerves of right, to the sharp cry as the filaments of taste are struck with a crashing sweep, is a range which no other instrument possesses.  A few exercises on it dally at home fit a man wonderfully for his habitual labors, and refresh him immensely as he returns from them.  No stranger can get a great many notes of torture out of a human soul; it takes one that knows it well,—­parent, child, brother, sister, intimate.  Be very careful to whom you give a side-door key; too many have them already.

——­You remember the old story of the tender-hearted man, who placed a frozen viper in his bosom, and was stung by it when it became thawed?  If we take a cold-blooded creature into our bosom, better that it should sting us and we should die than that its chill should slowly steal into our hearts; warm it we never can!  I have seen faces of women that were fair to look upon, yet one could see that the icicles were forming round these women’s hearts.  I knew what freezing image lay on the white breasts beneath the laces!

A very simple intellectual mechanism answers the necessities of friendship, and even of the most intimate relations of life.  If a watch tells us the hour and the minute, we can be content to carry it about with us for a life-time, though it has no second-hand, and is not a repeater, nor a musical watch,—­though it is not enamelled nor jewelled,—­in short, though it has little beyond the wheels required for a trustworthy instrument, added to a good face and a pair of useful hands.  The more wheels there are in a watch or a brain, the more trouble they are to take care of.  The movements of exaltation which belong to genius are egotistic by their very nature.  A calm, clear mind, not subject to the spasms and crises that are so often met with in creative or intensely perceptive natures, is the best basis for love or friendship.—­Observe, I am talking about minds.  I won’t say, the more intellect, the less capacity for loving; for that would do wrong to the understanding and reason;—­but, on the other hand, that the brain often runs away with the heart’s best blood, which gives the world a few pages of wisdom or sentiment or poetry, instead of making one other heart happy, I have no question.