'Men die of the diseases which they have studied most,' remarked the surgeon, snipping off the end of a cigar with all his professional neatness and finish. 'It's as if the morbid condition was an evil creature which, when it found itself closely hunted, flew at the throat of its pursuer. If you worry the microbes too much they may worry you. I've seen cases of it, and not necessarily in microbic diseases either. There was, of course, the well-known instance of Liston and the aneurism; and a dozen others that I could mention.'

...on opening the incubator I experienced one of those rare moments of intense emotion which reward the research worker for all his pains: at first glance I saw that the broth culture, which the night before had been very turbid was perfectly clear: all the bacteria had vanished... as for my agar spread it was devoid of all growth and what caused my emotion was that in a flash I understood: what causes my spots was in fact an invisible microbe, a filterable virus, but a virus parasitic on bacteria. Another thought came to me also, If this is true, the same thing will have probably occurred in the sick man. In his intestine, as in my test-tube, the dysentery bacilli will have dissolved away under the action of their parasite. He should now be cured.

Eradication of microbial disease is a will-o'-the-wisp; pursuing it leads into a morass of hazy biological concepts and half truths.

The Microbe is so very small,
You cannot make him out at all.
But many sanguine people hope
To see him down a microscope.
His jointed tongue that lies beneath
A hundred curious rows of teeth;
His seven tufted tails with lots
Of lovely pink and purple spots
On each of which a pattern stands,
Composed of forty separate bands;
His eyebrows of a tender green;
All these have never yet been seen
But Scientists, who ought to know,
Assure us they must be so ...
Oh! let us never, never doubt
What nobody is sure about!