"I can't do it," she cries desperately, wanting some release from this eternal, frustrating labour. "You can," says the midwife, "Now push hard," she commands. "Come on, push hard," says the midwifery student. "Yes, push hard," I say.

How can I possibly be in a position to give advice to a woman I have never met, experiencing pain I will never experience, in the course of a procedure which I have never seen before? I gulp and wait for the mother to turn to me slowly, fix me with a stare, and ask me if I will leave the room and let the people who know what they are doing get on with it. Fortunately, she seems to be more concerned with business at the other end of the bed to worry about me, whose most useful purpose is to stand rigidly at one side acting as a large white coated bedpost preventing her slipping too far to the right. I have got away with it.

I did think about the episode afterwards, partly because the authority I heard in my voice was worryingly believable. My voice had become slightly deeper, slower, and had a comforting tone to it. It was the kind of voice that, after a few years work, would be able to make the phrase "Just pop your clothes off behind the screen there" seem like the most everyday opener to a conversation.

A friend was telling me recently about a problem he was having with his sinuses and an operation that had been suggested. "What is an anterior ethmoidectomy?" he asked. I mumbled something about spaces in the skull clogging with mucus and the need to drain it. I then slowed and deepened my voice, and finished with the words, "But of course I'm sure it's a very safe procedure."

Safe procedure? What was I talking about? How could I know? But he was nodding wistfully. "Yes, that's much clearer now. It doesn't sound too bad does it?" I appeared to have succeeded in convincing him that having the inside of your skull fiddled with was a prospect to relish.

So I seem to be putting the cart of style before the horse of substance. I hope that I will soon learn some medical facts to prevent myself being landed in embarrassing situations with legal implications. But in the meantime I am objective about the words of others. When, after the delivery, the midwife said, in a warm, sincere tone: "You were very useful in there," of course I didn't believe her.

I started thinking about such matters when I read an article describing two male octopuses of different species who were caught on camera having sex with each other. I suppose there is not much to do down there in the cold and dark but that's no excuse for going out with the first thing with eight legs. The scientists say there is little action for a randy young octopus at the bottom of the sea, and so the creatures mate with any octopus that passes, regardless of sex or species, to ensure that when they get the correct combination the chance of procreation is not wasted.

But what has this to do with the meaning of life? Well it seems that the most important thing not just for octopuses but for the animal kingdom is to pass on genetic material. Nothing matters more than producing offspring because it's the only way of guaranteeing immortality. Maybe, deep down that's what drives humans as well. And so the meaning of life is ... life itself. Forget the distractions. However full a life you have led, if you have no progeny then you have missed the whole point.

By the time you have read this article there will be an extra 2000 people in the world. Global population is rising at an alarming rate. In 25 years there will be another 2.5 billion of us, and there is no guarantee that the planet will cope. The only solution is for us to have fewer children. Have we cheated nature with all our advances and forced ourselves into a meaningless existence? As I looked at baby Amy I wondered how many others were born at the same time around the globe. One more life doesn't really matter, does it?

I am not happy when the bell rings. I am not ready to move to the next station as I haven't finished this one yet. But I must leave the arteriogram, abandoning my list of internal iliac artery branches. Why did I manage to name only a few of the obscure ones and none of the biggies?

It's a spleen. I recognise it and am quite chuffed, until I'm asked which border the pink pin is in. I remember now that I missed the day when we removed the spleen from our body, and I really am not sure how it sits in situ. I saw it the next day, lying forlornly on the chest of our cadaver and I remember something about red gunk and white gunk. Hmm, that was the really sunny day when we had a bit of snow left and I'd decided that catching the last of the sledging conditions was preferable to dissection .... The bell rings. I kick myself and vow never to miss anything ever again.

Agghh, it's a microscope. I had a nightmare about dancing pink cells last night. Deep breath, quick glance. It's glandular, I think, could be testis or breast. Great.

Second part to the question asks which hormones act on the structure. Maybe I could cover myself by hazarding a guess at testis and then answer prolactin. Or would they just think me a complete fool and not credit me with either mark?

Ting ting, and on we go. The next question is much better - I know a stomach when I see one, and the parasympathetic action on the pyloric sphincter - or do I? I sneak furtive glances across at people I know. One of my friends is doing some elaborate contortionist stuff to get round the other side of a liver in an attempt to orientate himself. We are not allowed to move the objects, and he has a knee on the table and his neck bent double. I stifle a giggle as he gets too close, and a waft of formalin almost sends him crashing head first into the right lobe. Ting ting and it's another microscope.

My eyesight is worse than the candidate before me, and as I fumble to focus the stubborn instrument I accidentally knock the platform and lose the field I'm supposed to be looking at. I am staring intently, head pressed to the eyepieces, as my pencil tin slips unassumingly from my white coat and clatters to the floor. I leap out of my skin, taking my eyes out on the microscope as I do so. Trying to ignore the glares of my colleagues, and my escaping pens, I rub my bruised eyes in an attempt to see again. Come on, concentrate, focus, look at the slide.

The bell tinkles and I scowl at the nasty man once more. I hadn't even read the question.

Lastly, I turned to pet number three, a snappy little dog. A result - loud irregular thumping. History? Bad tempered, prone to flying into fits of rage and almost knocking himself out "killing" his various toys. Breathless at rest until a recent crash diet.

I listened again. "Irregularly irregular - atrial fibrillation, digoxin" popped into my head. My parents listened in turn. They didn't like what they heard. Why didn't his heart go b-boom b-boom? Maybe it's something dogs do I said, not convinced. Should they give him his chocolate drop stocking or would the cholesterol kill him? Young adults get a similar thing when they breathe in and out I said trying to sound jolly. But the dog is old and obviously I was making this breathing thing up to keep the dreadful truth from them.

My parents worried increasingly - their dog had heart disease. The dog revelled in the gloom and moped about whenever my parents were looking. My mother didn't want to bother the vet and there was no point ringing for an appointment after Christmas as it was obvious the dog wouldn't last that long. At least his last Christmas would be a happy one. Finally on Christmas Eve I could stand it no longer and took the dog to the vet myself.

At the vets the patient underwent a Jeckyl and Hyde-like transformation (has anyone done any studies on the vet-patient relationship?), cowering and trembling on the table as though used to regular beatings and making a complete mockery of the dog muzzle my mother had insisted I put on him.

Yes, the vet agreed, the rhythm was irregular. You think it's atrial fibrillation, don't you, she said. Well, at least she didn't laugh. It's just sinus arrhythmia, you can hear the heart changing rate as he breathes - it's common in dogs.

Still it wasn't an entirely wasted journey, the dog's angelic behaviour meant that the stinking breath could be investigated. So I came back with some antibiotics (sicked up following too much chocolate and duck on Christmas Day) for the rotting teeth and the dog celebrated its return to good health and habitual psychosis by attacking one of the cats.