"Just as the only reservoir for the typhus virus in nature is provided by man, so the only vector of infection is the louse. The bite of the louse is not virulent immediately after the infecting meal. It becomes so only towards the 7th day following infection"

In this quote, Charles Jules Henry Nicolle is talking about the transmission of the typhus virus. He discusses that the only location where the virus can endure in nature is within the human body. Furthermore, he mentions that the only way the infection can spread from a single person to another is through the bite of a louse. However, Nicolle clarifies that the louse does not instantly become infectious after eating an infected individual. It takes about 7 days for the louse to end up being virulent and capable of transmitting the virus to another individual. This highlights the value of comprehending the life process of the louse in preventing the spread of typhus.