How well Doctor Holmes understands the "mechanism" of verse may be seen from his Physiology of Versification and the Harmonies of Organic and Animal Life, a valuable article published in the Boston Medical and Surgical Journal of January 7, 1875.

"Respiration," he says, "has an intimate relation to the structure of metrical compositions, and the reason why octosyllabic verse is so easy to read aloud is because it follows more exactly than any other measure the natural rhythm of the respiration....

"The ten syllable, or heroic line has a peculiar majesty from the very fact that its pronunciation requires a longer respiration than is ordinary.

"The cæsura, it is true, comes in at irregular intervals and serves as a breathing place, but its management requires care in reading, and entirely breaks up the natural rhythm of breathing. The reason why the 'common metre' of our hymn books and the fourteen syllable line of Chapman's Homer is such easy reading is because of the short alternate lines of six and eight syllables. One of the most irksome of all measures is the twelve-syllable line in which Drayton's Polyolbion is written. While the fourteen syllable line can be easily divided in half in reading, the twelve syllable one is too much for one expiration and not enough for two, and for this reason has been avoided by poets.

"There is, however, the personal equation to be taken into account. A person of quiet temperament and ample chest may habitually breathe but fourteen times in a minute, and the heroic measure will therefore be very easy reading to him; a narrow-chested, nervous person, on the contrary, who breathes oftener than twenty times a minute, may prefer the seven-syllable verse, like that of Dyer's Grongar Hill, to the heroic measure, and quick-breathing children will recite Mother Goose melodies with delight, when long metres would weary and distract them.

"Nothing in poetry or in vocal music is widely popular that is not calculated with strict reference to the respiratory function. All the early ballad poetry shows how instinctively the reciters accommodated their rhythm to their breathing: Chevy Chace, or The Babes in the Wood may be taken as an example for verse. God save the King, which has a compass of some half a dozen notes, and takes one expiration, economically used, to each line, may be referred to as the musical illustration.

"The unconscious adaptation of voluntary life to the organic rhythm is perhaps a more pervading fact than we have been in the habit of considering it. One can hardly doubt that Spenser breathed habitually more slowly than Prior, and that Anacreon had a quicker respiration than Homer. And this difference, which we conjecture from their rhythmical instincts, if our conjecture is true, probably, almost certainly, characterized all their vital movements."

So much for the bare vehicle of verse, but the poet himself, as Doctor Holmes says in his review of "Exotics," is a medium, a clairvoyant. "The will is first called in requisition to exclude interfering outward impressions and alien trains of thought. After a certain time the second state or adjustment of the poet's double consciousness (for he has two states, just as the somnambulists have) sets up its own automatic movement, with its special trains of ideas and feelings in the thinking and emotional centres. As soon as the fine frenzy, or quasi trance-state, is fairly established, the consciousness watches the torrent of thoughts and arrests the ones wanted, singly with their fitting expression, or in groups of fortunate sequences which he cannot better by after treatment. As the poetical vocabulary is limited, and its plasticity lends itself only to certain moulds, the mind works under great difficulty, at least until it has acquired by practice such handling of language that every possibility of rhythm or rhyme offers itself actually or potentially to the clairvoyant perception simultaneously with the thought it is to embody. Thus poetical composition is the most intense, the most exciting, and therefore the most exhausting of mental exercises. It is exciting because its mental states are a series of revelations and surprises; intense on account of the double strain upon the attention. The poet is not the same man who seated himself an hour ago at his desk with the dust-cart and the gutter, or the duck-pond and the hay-stack, and the barnyard fowls beneath his window. He is in the forest with the song-birds; he is on the mountain-top with the eagles. He sat down in rusty broadcloth, he is arrayed in the imperial purple of his singing robes. Let him alone, now, if you are wise, for you might as well have pushed the arm that was finishing the smile of a Madonna, or laid a veil before a train that had a queen on board, as thrust your untimely question on this half-cataleptic child of the Muse, who hardly knows whether he is in the body or out of the body. And do not wonder if, when the fit is over, he is in some respects like one who is recovering after an excess of the baser stimulants."

As a writer of humorous poetry, it is safe to say that Oliver Wendell Holmes is without a peer.