I had completed enough experimental work for my doctoral thesis by Easter 1931 and I returned then to Scotland to shake off the after-effects of a severe attack of influenza. I returned to Frankfurt a couple of months later to submit my thesis and take my Dr. phil. nat. examination. The examination was oral and was in three parts: (a) a one-hour oral on organic chemistry, (b) half an hour on physical chemistry and (c) half an hour on mineralogy, the examination in each section being conducted by the appropriate professor in the presence of an umpire - in my case the professor of physics who occupied the time by reading the Frankfurter Zeitung. Although the examination was public, one never had an audience of more than two or three and these were simply men who were intending to take their examination shortly and wanted to see what kind of punishment to expect. There was a curious ritual associated with the Doktorexamen in Frankfurt (and probably elsewhere in Germany) at that time. About a week before the date of the examination one called on each of the examining professors at his home bearing a bunch of flowers for his wife, and had a chat. Although the chat was largely given over to pleasantries with the professor of your main subject - in my case Borsche -the visits to the other professors were much more important. It was accepted that a candidate would probably not be expert over the whole area covered by his subsidiary subjects and so one was expected to indicate those parts in which one was most interested (i.e. knew something) and those in which one was less interested (i.e. knew nothing). This pretty custom was intended to, and usually did, avoid embarrassment to both parties in the examination. As a matter of fact it didn't work out too well for me in physical chemistry. Bonhoeffer had come to Frankfurt - his first full professorship - at about the time that I did; being in any case a rather absent-minded young man, and still rather unaccustomed to examining, he confused what I had described to him a week before as interesting and uninteresting. Accordingly, I had a rough half-hour on pre-dissociation spectra and some other photochemical topics based on a lecture course through which I had usually slept since it was given twice weekly at 5 p.m. in the summer semester after I had been swimming in the Stadtwald since lunchtime. However not too much damage was done since, at the end of the day, my ' Note' for the thesis was ' Ausgezeichnet' and for my oral examination 'Sehr gut'. My other subsidiary, mineralogy, had been chosen by me partly because I had some little acquaintance with the subject from my Glasgow course in geology, and partly because it shared with bacteriology the reputation of being the easiest option in the faculty; bacteriology lectures, however, were given in the hospital located on the other side of the city which made my final choice a simple one.
In opting for mineralogy I chose better than I knew. It turned out that Nacken, the professor in Frankfurt, was a great admirer of Gregory, the geologist in Glasgow, and seemed to consider any pupil of Gregory as a positive asset to his department. Accordingly Morrison and I were welcomed with open arms and our pathway through the subject was made very easy; Bertie Blount also benefited from this for, although he knew no mineralogy at all, it was assumed that, since he came with me to be interviewed, he too must be a Gregory pupil!
I was much impressed by the oral examination for the doctorate which, especially in the principal subject, was quite searching. The technique - which was customary and did not apply simply to my case - was to ask a question of the candidate and see whether from his opening reply he really knew something about the topic at issue. If he did, the examiner passed rapidly to another topic; if not, the candidate was subjected to more probing so that his knowledge or lack of it could be ascertained. In this way it was possible to cover a very great amount of ground in the course of an hour and an experienced examiner could find out much more than he could have done by means of written papers. One is often told how students in German universities tended to wander from one university to another during their courses. This may well have been true in some places, but it did not seem to be the case in Frankfurt save in the following special circumstances. It was generally held that, if it became clear to you that you were likely to fail in your examination, the proper thing to do was to transfer to the University of Giessen for your last semester; this was in fact done from time to time by the weaker vessels.
Looking back now, my recollection is that my life as a student in Frankfurt was a very happy one. No doubt matters were helped by the fact that, having apparently a certain facility for languages, I acquired fluency in German rapidly and so was able to get to know people much better than would otherwise have been possible. The student body was pretty cosmopolitan comprising, as it did, many impoverished young men from Eastern European countries belonging to the old Austro-Hungarian Empire, with a sprinkling of Russians, both emigres and Soviet engineering students, Persians and other Middle Easterners with a few Americans but, as far as I could ascertain, no British students other than ourselves. Frankfurt had taken over the colours and traditions of the German University of Strassburg including its student corporations, although it still retained its designation 'Preussiche Staats-Universitat zu Frankfurt a.M.' So it was that, although duelling was illegal, Frankfurt, in my day, still had several of the old fighting corporations. My friend Morrison had rooms in the same house as one Otto Lochel, president of one of these, the 'Freie Landsmannschaft Franco-Saxonia', and we became quite friendly with him. In due course we were admitted as honorary ' Freie Landsmanner' and used to attend from time to time the weekly Kneipe or club meeting complete with our song books and ribbons all in the orange and silver colours of the Landsmannschaft. These meetings were devoted mainly to singing and beer drinking and were relatively peaceful, although I recall on one occasion there was a row over some girl which led to a sabre duel. Duelling occurred at rather infrequent intervals and was usually the traditional 'Mensur' in which the contestants' sole object was to give one another a few facial scars. I did attend one of these events. It was held at 5 a.m. in the yard of an inn in Sachsenhausen, round which we had a series of scouts posted on the look-out for police. This particular 'Mensur' had been arranged with the Darmstadt branch of the Franco-Saxonia which had sent up two or three of their latest recruits (Fuchse), all of them freshmen at the Technische Hochschule, to swap scars with our recruits. It was a curious performance - almost a ritual - each duel being stopped by the attendant doctor as soon as a suitable face wound had been inflicted. At the end of it all we repaired to the inn and despite the early hour consumed vast quantities of beer before returning to Frankfurt. Nevertheless, contacts such as these with 'Korpstudenten' from the various corporations put me much more in touch with the student body than would otherwise have been possible. Most of the students I knew were right wing in their political stance although few of them were extreme. For the most part they sympathised with the democratic National Party; it was only later as the Weimar Republic finally began to collapse that they moved over mainly to the National Socialist Party. Franco-Saxonia apart, we lived the normal student life. In those days Frankfurt was an attractive city with its spacious west end and its dignified central area within the Anlagen: south towards the river lay the beautiful Altstadt with its Weinstuben which we used to frequent when we were feeling moderately affluent. Alas, all that has gone since the Second World War, and the Frankfurt I knew has been replaced by a rather featureless modern city with hardly any of its old character.