Professor Denny Mitchison, gets up at 6.30am most weekdays and by 8 o'clock, he is in his office at the University of London. He recently decided that, at the age of 90, he might just allow himself Mondays off. He owes position as the oldest full-time professor in the country to his refusal to give up when there is still work to be done.
In his view : "Science is a lifetime occupation. It takes you over. When you actually find something new, it's the most exciting time. The real reason one goes on doing it is simply having put all that amount of one's self into something. If you then stopped doing that, it would all go. You can look at it and say, how many lives have you saved? It's probably in the millions."
He is not exaggerating. In 1946, as a young pathologist at the Brompton Hospital in London, he pioneered clinical trials of the anti-TB drug streptomycin, a disease which killed 50% of those it afflicted and the only treatment offered was bed rest.
The trials were a success, and were the start of decade after decade of breakthroughs. The regimen of drugs he devised while working in the 60's and 70's is still the standard model used today and he is currently involved in setting up clinical trials that could reduce the time of drug treatment for TB from six to four months. His colleagues, who describe him as a 'living legend', think he should get a Nobel prize.
These days, his teaching role is limited, but he still lectures undergraduates on the treatment of TB at the University . He despairs that students are no longer widely trained in the 'hands-on' laboratory techniques of microbiology.
"The reason it's stopped is to a large extent because the Health and Safety Executive comes along and says it's too dangerous for students to deal with real bacteria. But this is the way people got trained. They don't get trained now. It's a huge loss."
He talks about the "abominable" impact of regulation, but in the early days when safety precautions were "absolutely useless", he himself contracted mild TB, which kept him off work for about six months.
"What we did was only possible because of the absence of regulation. At that time there were no ethics committees, no licensing bodies, you didn't have to get permission to do anything. No formalities at all. Nowadays it's totally impossible. Medicine is being brought to a halt by too much regulation, because people who would in the past have done clinical trials, advanced work, just can't do it now. It's too difficult, too expensive. It's a very, very gloomy outlook."
As the grandson of the great physiologist JS Haldane, who made crucial discoveries about the effects of gases on the human body via experiments such as starving himself of oxygen in sealed chambers, and the nephew of the geneticist and evolutionary biologist JBS Haldane, he feels he was pretty much born into science.
When he first arrived at Cambridge University, he was more interested in politics than studies, which is not surprising, since his father was the Labour politician, Dick Mitchison (on the left) and he held "very leftwing" views. At first he was "extremely bad at exams and learning".
"Then in a year I really got from being right at the bottom of the class to right at the top. I had some very bad results and I thought 'I really must do some work', so I did, and people said "he's the brightest science student we've got".
"It's really about whether you want to learn. There's a fundamental difference between being taught and learning yourself, which is what you've got to do to reach a really high standard."
For all his determination not to stop working, Mitchison suspects his age does make it harder to get funding from granting authorities. "I think it's natural in a way that this sort of thing happens because I can't say I'm going to be alive in three years".
Does teaching undergraduates make him feel a bit old? Apparently not : "I feel a little bit more experienced, but as you grow older you don't actually feel older. You feel pretty young, except some of your functions aren't as good as they used to be. That's the secret to doing this, go on behaving as you normally would and you actually don't get older."
He confesses that he rarely stops thinking about his work. "It used to be said that you had your best thoughts in the bath, but I've stopped taking them because I can't get out. Showers don't last long enough to think in, so the most productive time often is some time in the middle of the night. You can let your mind do a bit of roaming around. The problems never go away. There are always fresh problems, science is like that, you never solve them all."
"Nobody in my family in the scientific part ever retired. Well I might, if I get very ill. But how do you give up a whole major part of your life? I view it soberly, but it's a lot of achievement, and I continue to have what I think are really quite interesting and important ideas."
He stands as an inspiration to us all, young and old.