Studies in the Virgin Islands, Labrador, and Alabama, suggest that colds are incited by some specific agent with which we are not yet familiar. They suggest also that the secondary and more severe symptoms associated with colds may be due to certain aerobic flora commonly found in the nasopharynx. Types of pneumococci which are virulent (to white mice) and true Pfeiffer's bacilli requiring both V and X substance (and forming indol?) seem to be of particular importance in these secondary infections.
The studies indicate that the specific agent which initiates colds is infectious in nature, and spread by direct contact, with an incubation period of 1 to 3 days. There is strong evidence that environmental factors, particularly reduction in atmospheric temperature, have some influence upon the incidence of colds.