Of all the problems which were open to me for study, typhus was the most urgent and the most unexplored. We knew nothing of the way in which contagion spread.

I finally demonstrated that typhus infection is not hereditary in the louse.

Most of the doctors in the Tunisian administration, especially those in country districts, contracted typhus and approximately one third of them died of it.

The fact that I was fortunate enough to escape contagion, in spite of frequent, sometimes daily contacts with the disease, was because I soon guessed how it spread.

It did not seem likely that I was destined to undertake research on typhus.

My first attempts to transmit typhus to laboratory animals, including the smaller species of monkeys, had failed, as had those of my predecessors, for reasons which I can easily supply today.