In Literary Criticism: A Short History (1957) by Cleanth Brooks and his Yale colleague, William Wimsatt, a pointer to McLuhan’s 1943 PhD thesis appears in its preface:

A more or less pervasive debt in several chapters to a manuscript book by H.M. McLuhan concerning the ancient war between dialecticians and rhetoricians is here gratefully acknowledged and is underscored by the quotation, following chapter 4, of two substantial excerpts from published essays by Mr. McLuhan.

The excerpts were taken from ‘Edgar Poe’s Tradition’, Sewanee Review, LII (January-March, 1944) and ‘Sight, Sound and the Fury’, Commonweal, LX (April 9, 1954):

Edgar Poe’s Tradition
This tradition [the oratorical]¹ has been a continuous force in European law, letters, and politics from the time of the Greek sophists. It is most conveniently referred to as the Ciceronian ideal, since Cicero gave it to St. Augustine and St. Jerome, who in turn saw to it that it has never ceased to influence Western society. The Ciceronian ideals as expressed in the De Oratore or in St. Augustine’s De Doctrina Christiana is the ideal of rational man reaching his noblest attainment in the expression of an eloquent wisdom. Necessary steps in the attainment of this ideal are careful drill in the poets followed by a program of encyclopedic scope directed to the forensic end of political power. Thus, the doctus orator is, explicitly, Cicero’s sophistic version of Plato’s philosopher-king. This ideal became the basis for hundreds of manuals written by eloquent scholars for the education of monarchs from the fifth century through John of Salisbury and Vincent of Beauvais, to the famous treatises of Erasmus and Castiglione. (…)
So far as America is concerned, this was a fact of decisive importance, since Virginia, and the South in general, was to receive the permanent stamp of this Ciceronian ideal. (…) It is thus no accident that the creative political figures of American life have been molded in the South. Whether one considers Jefferson or Lincoln, one is confronted with a mind aristocratic, legalistic, encyclopedic, forensic, habitually expressing itself in the mode of an eloquent wisdom. (…)
New England is in the scholastic tradition, and profoundly opposed to “humanism.” Briefly, the theocratic founders of Harvard and rulers of New England were Calvinist divines, fully trained in the speculative theology which had arisen for the first time in the twelfth century the product of that dialectical method in theology which is rightly associated with Peter Abelard. Unlike Luther and many English Protestants, Calvin and his followers were schoolmen, opposed to the old theology of the Fathers which Erasmus and humanist-Ciceronians had brought back to general attention after the continuous predominance of scholastic theology since the twelfth century. To the humanists nobody could be a true interpreter of Scripture, a true exponent of the philosophi Christi, who had not had a full classical training. So Catholic and Protestant schoolmen alike were, for these men, the “barbarians,” the “Goths of the Sorbonne,” corrupting with “modernistic” trash (the schoolmen were called moderni from the first) the eloquent piety and wisdom of the Fathers. (The Fathers were called the “ancients” or antiqui theologi.) (…)
Harvard, then, originated as a little Sorbonne, where in 1650 the scholastic methods of Ockham and Calvin, as streamlined by Petrus Ramus, were the staple of education. Logic and dialectics were the basis of theological method, as of everything else at Harvard. Here rhetoric was taught, not for eloquence, but in order to teach the young seminarian how to rub off the cosmetic tropes of Scripture before going to work on the doctrine with dialectical dichotomies. Ramus taught a utilitarian logic for which he made the same claims as pragmatists do for “scientific method.” In fact, Peirce, James and Dewey could never have been heard of had they not been nurtured in the Speculative tradition of the scholastic theologians Calvin and Ramus.²

Sight, Sound and the Fury
Until Gutenberg, poetic publication meant the reading or singing of one’s poems to a small audience. When poetry began to exist primarily on the printed page, in the seventeenth century, there occurred that strange mixture of sight and sound later known as “metaphysical poetry” which has so much in common with modern poetry. (…)
The printed page was itself a highly specialized (and spatialized) form of communication. In 1500 A.D. it was revolutionary. And Erasmus was perhaps the first to grasp the fact that the revolution was going to occur above all in the classroom. He devoted himself to the production of textbooks and to the setting up of grammar schools. The printed book soon liquidated two thousand years of manuscript culture. It created the solitary student. It set up the rule of private interpretation against public disputation. It established the divorce between “literature and life.” (…)
We have long been accustomed to the notion that a person’s beliefs shape and color his existence. They provide the windows which frame, and through which he views, all events. We are less accustomed to the notion that the shapes of a technological environment are also idea-windows. Every shape (gimmick or metropolis), every situation planned and realized by man’s factive intelligence, is a window which reveals or distorts reality. Today, when power technology has taken over the entire global environment to be manipulated as the material of art, nature has disappeared with nature-poetry. (…)
From the point of view of its format, the press as a daily cross-section of the globe is a mirror of the technological instruments of communication. It is the popular daily book, the great collective poem, the universal entertainment of our age. As such it has modified poetic techniques and in turn has already been modified by the newer media of movie, radio, and television. These represent revolutions in communication as radical as printing itself. (…)
James Joyce was the first to seize upon newspaper, radio, movie, and television to set up his “verbicovisual” drama in Finnegan’s Wake. Pound and Eliot are, in comparison with Joyce, timid devotees of the book as art form. (…)
in cognition we have to interiorize the exterior world. We have to recreate in the medium of our senses and inner faculties the drama of existence. This is the world of the logos poietikos, the agent intellect. In speech we utter that drama which we have analogously recreated within us. In speech we make or poet the world even as we may say that the movie poets the world. Languages themselves are thus the greatest of all works of art. They are the collective hymns to existence. For in cognition itself is the whole of the poetic process. But the artist differs from most men in his power to arrest and then reverse the stages of human apprehension. He learns how to embody the stages of cognition (Aristotle’s “plot”) in an exterior work which can be held up for contemplation. (…)
It is only common sense to recognize that the general situation created by a communicative channel and its audience is a large part of that in which and by the individuals commune. The encoded message cannot be regarded as a mere capsule or pellet produced at one point and consumed at another. Communication is communication all along the line. One might illustrate from sports. The best brand of football played before fifty people would lack something of the power to communicate. (…)
What we have to defend today is not the values developed in any particular culture or by any one mode of communication. Modern technology presumes to attempt a total transformation of man and his environment. This calls in turn for an inspection and defense of all human values. And so far as merely human aid goes, the citadel of this defense must be located in analytical awareness of the nature of the creative process involved in human cognition. For it is in this citadel that science and technology have already established themselves in their manipulation of the new media.³