The correspondents are:
Professor O Maaløe (reference strains of E. coli), Dr B E H Maden, Dr Walter M Macintyre, Dr J T Madison, Dr Beatice S Magdoff, Michael Magzis (Alfred A Knopf, Jacques Monod), Dr G P Di Mayorca, Group Captain John E Malcolm (Korotkov's sounds), Dr H Malke, Nicolas Malleson (LSD), Dr Bo G Malmström, Rattan Singh Mann, Robert Manning (Atlantic Monthly), Professor Clyde Manwell (cannabis), Dr Julius Marmur, Dr David Marr, Dr Paul A Marks, Dr R G Martin, Professor Theodor Martinec, Virginia E Marting (includes cutting on chapel for Churchill College), Dr Charles Mayer, Dr R A McConnell, Professor A I McMullen, Dr Kenneth McQuillen (Churchill College), Sir Peter Medawar, Dr Zh A Medvedev, Professor W J Ganshof van der Meersch, Dr Jagdish Mehra, J Mehrishi, Josef Mertens (letter in German), Dr Matthew Meselson (biological warfare), Bernard Miles (The Molecule Club), Dr H Todd Miles, Dr P H Millar, Karl Miller (The Listener, Rickman Godlee Lecture), Dr Beatrice Mintz, Dr R Monier (5S RNA), Dr Robin Monro, Dr A Monroy, M F Moody, Ruth Moore, Dr Stanford Moore, Professor M Moraza, S A Morell, Dr R S Morgan (EDSAC, models), Dr Harold J Morowitz, John Mosely, Dr A J Munro, and Dr V V Murthy (the Soul).
One letter in German (Mertens).