The mouth of the child is unclean and harbors numbers of the same sort of organisms as those causing the lung inflammation; but in the absence of such a mode of infection as is given by spray formation it is difficult to see how the extension from the mouth to the lungs could take place.

The weakened condition of the body in these cases favors the secondary infection.
If the disease be located in the intestines, as in typhoid fever and dysentery, the organisms are contained in the fecal discharges, and by means of these the infection is extended.

In typhoid fever, dysentery and cholera massive infections of the populace may take place from the contamination of a water supply and the disease be extended over an entire city.

One of the most striking instances of this mode of extension was in the epidemic of cholera in Hamburg in 1892.

There were two sources of water supply, one of which was infected, and the cases were distributed in the city in the track of the infected supply.