Germs may be carried from one person to another, and received by that person in different ways. They may be conveyed by actual contact, as in the case of ringworm, erysipelas, ophthalmia (infectious inflammation of the eyes), hydrophobia, small-pox, etc. The germs may possibly be taken in through the unbroken skin, but much more frequently through a small crack or sore in the skin. Secondly, they may be conveyed by the air, and taken in by the breath. This is by far the commonest method, as seen in whooping-cough, scarlatina, small-pox, diphtheria, measles, consumption, etc. Thirdly, they may be carried by water, and so taken into the stomach and intestines, as with cholera, typhoid fever, dysentery, etc. Fourthly, by the food, and taken to the stomach and intestines as before, as with typhoid fever, consumption, and foot-and-mouth disease (conveyed by milk). Fifthly, they may be carried by clothes, and so get into the air, as with scarlatina. They may also be carried by insects, such as flies and mosquitoes, as above stated. In some instances the method of conveyance is mysterious, as in the widely-prevalent influenza, whose history has so far baffled research.