In the bright light of medical science's triumph over typhus in Tunisia, Ernest Conseil was haunted by a growing shadow of doubt. It was not that he had reservations about the transmission discovery per se: even if some medical researchers remained unpersuaded by evidence of the louse's unique role in spreading typhus, the insect was, Conseil believed, the disease's vector. It was the way the louse transmitted typhus that concerned him. Nicolle had announced with great fanfare that lice spread typhus by biting their victims. Indeed, he had waited to make his announcement about the path of typhus spread until he had successfully transmitted the disease between monkeys through louse bites. Nicolle had put great stock in this formulation for at least two reasons. First, as we have seen, he believed the bite experiment to be the final, crucial step in demonstrating the course taken by “nature” itself in spreading typhus. Second, he used it to substantiate a specific program of “rational hygiene” against the disease. Secure in the knowledge that typhus was propagated in nature only by the louse's bite—not by its droppings or, as he would soon assert, by hereditary transmission to offspring— Nicolle could confidently focus on killing living lice to control the disease. It is therefore understandable that, when Conseil approached him with his concerns, Nicolle was skeptical.

In the spring of 1914, a new collaborator arrived at the IPT. Georges Blanc had, like Ludovic Blaizot, worked in Blanchard's parasitology lab at the Paris Faculty of Medicine; like Blaizot, Blanc, too, was interested in spirochetes. His arrival in Tunisia corresponded with the “importation” of three typhus cases into Tunis, and Nicolle set him to work with Conseil to relieve the latter's nagging doubts about the route the disease took in moving from louse to human.