His book influenced physicians and public health officials across United States and Europe by demonstrating the central importance of the human carrier who does not have the symptoms of the disease but carries the germs and spreads it .
His book is the Sources and Modes of Infection .
His book , The Sources and Modes of Infection , influenced physicians and public health officials across United States and Europe by demonstrating the central importance of the human carrier who does not have the symptoms of the disease but carries the germs and spreads it .