From the practical point of view, the susceptibility to infection of the guinea pig proved to be the most useful step forward. Today, all laboratories use this animal for preserving the virus.
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.
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.
The discovery that I soon made that the guinea pig was also susceptible to infection made it possible for me, from the third year on, to preserve the virus on this animal.