And this is the ultimate lesson that our knowledge of the mode of transmission of typhus has taught us: Man carries on his skin a parasite, the louse. Civilization rids him of it. Should man regress, should he allow himself to resemble a primitive beast, the louse begins to multiply again and treats man as he deserves, as a brute beast. This conclusion would have endeared itself to the warm heart of Alfred Nobel. My contribution to it makes me feel less unworthy of the honour which you have conferred upon me in his name.

The native hospital in Tunis was the focal point of my research. Often, when going to the hospital, I had to step over the bodies of typhus patients who were awaiting admission to the hospital and had fallen exhausted at the door. We had observed a certain phenomenon at the hospital, of which no one recognized the significance, and which drew my attention. In those days typhus patients were accommodated in the open medical wards. Before reaching the door of the wards they spread contagion. They transmitted the disease to the families that sheltered them, and doctors visiting them were also infected. The administrative staff admitting the patients, the personnel responsible for taking their clothes and linen, and the laundry staff were also contaminated. In spite of this, once admitted to the general ward the typhus patient did not contaminate any of the other patients, the nurses or the doctors. I took this observation as my guide. I asked myself what happened between the entrance to the hospital and the wards. This is what happened: the typhus patient was stripped of his clothes and linen, shaved and washed. The contagious agent was therefore something attached to his skin and clothing, something which soap and water could remove. It could only be the louse. It was the louse.