I found this extremely irritating, especially when, as later, he asserts that in religious paintings Christ’s cock is often shown erect. Where? When? By whom? The Professor does not say. But given the Christian attitude to sex, such an approach would have consigned both painter and painting to the flames. Again, it is a shock to be told, without references, that St Joseph, apparently the patron saint of marriage, is depicted as decrepit and a virgin. Try getting your brain round that one.

The high points of comedy in his book, for which you have to dig, come when you get on to those periods when head-bangers roamed the earth, in other words, the Middle Ages, the time of Victoria and the 20th century.

The medieval church (‘priests’, says the Professor) believed that there were two sure-fire seduction techniques open to women. One was to feed men bread which they had kneaded with their buttocks. He does not go into the practical problems involved (but then priests and professors have never kneaded bread. I have). The other was to stuff fish up inside themselves, then cook this. What kind of fish?

The Victorians, or at least those who wrote on the subject, believed men had only a finite reservoir of semen which had to be husbanded (nice irony, that). It was not just a matter of conservation; the stuff leaked out (which meant that well into the 20th century libertines like Frank Harris tied cords round their cocks). Circumcision was extolled as a means of preventing masturbation.

Then there was Kinsey who did not believe in conservation at all but in the principle of ‘use it or lose it’, and directed his researchers into multiple use with volunteers. For sex had come into the laboratory. A scientist injected himself with the crushed testicles of dogs and guinea pigs and claimed this made him pee 25 per cent further. In 1983 an English scientist, addressing a learned conference in Las Vegas, of all places, on the erectile effect of direct injections into the cock, cheerfully dropped his trousers and gave a demonstration.

Somehow amongst these shenanigans discoveries got made, often by accident. The vasectomy, initially pioneered in the 1890s as a cure for prostate trouble, became in the 1930s commercially successful as a recipe for rejuvenation (Yeats had it done), and of course now is a contraceptive. Doctors do not come well out of this account.

Nor does anyone else. There was the myth of the cervical orgasm fostered by Marie Stopes, and of the vaginal orgasm, the big one, a sort of Grail still believed in by my generation, whom it torments, even though this is impossible, the vagina having no nerve endings. Like America, the clitoris was discovered many times, usually by male doctors (presumably women knew it was there all the time, but didn’t think it worth mentioning).

What comes over in this book is how little is still known about sex, or perhaps how little there is to be known, even after all those electrodes. Also the refinements of cruelty it allows couples, a woman smoking during the act, a man, as instructed, gloomily studying the wallpaper to postpone orgasm.

It is the sadness I shall remember most.

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