The ideal reasoner, he remarked, would, when he had once been shown a single fact in all its bearings, deduce from it not only all the chain of events which led up to it but also all the results which would follow from it.

Well, I'm a bacteriologist, you know. I live in a nine-hundred-diameter microscope. I can hardly claim to take serious notice of anything that I can see with my naked eye.

Circumstantial evidence is a very tricky thing. It may seem to point very straight to one thing, but if you shift your own point of view a little, you may find it pointing in an equally uncompromising manner to something entirely different

There are heroisms all round us waiting to be done.

Why should people ever take credit for charity when they must know that they cannot gain as much pleasure out of their guineas in any other fashion?

I am a brain, Watson. The rest of me is a mere appendix.

‎A change of work is the best rest.