If the disease is measles, one may expect a general epidemic, since its power of direct contagion is nearly equal to scarlet fever, although the fatality is much less. It is unfortunate that so little pains are taken to prevent the spread of this disease and fortunate that, except in the case of very young children, the effect of the illness is only a temporary inconvenience. Curiously, however, if measles attacks savage tribes where it has been before unknown, the severity of the disease is very great. Cases are on record where measles have broken out on the frontier and whole villages were wiped out; where the insignificant measles, so innocuous in civilized communities, became a plague similar to a scourge of the Middle Ages. It apparently has been modified by its passage through generations of individuals, just as any bacterial disease germ is modified by successive transmission through the bodies of different animals. When, however, the disease breaks out in a community which has not suffered from the disease for many years, it is, on that account, likely to appear in a far more virulent form. _Characteristic eruptions of measles._ Measles, like scarlet fever and chicken pox, is an eruptive disease; that is, is accompanied with a rash, differing slightly in the three diseases of which the presence of the rash and its progress over the body is one of the distinguishing features. In scarlet fever, for instance, the rash appears first on the neck and chest or back and spreads outward to the extremities. In measles, the rash appears on the extremities, beginning on the face usually, and spreads to the chest and trunk. In scarlet fever, this rash appears as fine scarlet pin points scattered around on the reddened skin, and on the second or third day the entire body may look like a boiled lobster. In measles, the rash appears as blotches, while the skin is not flushed but retains its natural color. In chicken pox, the rash appears generally on the body first and consists of small red pimples which develop into whitish blisters about as large as a pea and well separated. They are much more distinct and separated than the rash of scarlet fever and measles, and are much more likely to be mistaken for smallpox pustules than for an ordinary eruptive rash.