There are four diseases, scarlet fever, measles, whooping cough, and chicken pox, which are recognized as belonging preeminently to the period of childhood and which are supposed to be the result of bacterial contagion, although, curiously, the specific bacteria concerned in any one of these four diseases has not been detected. They may be rationally grouped together for two reasons. First, because of their attacking, in the majority of cases, children under the age of fifteen years, and second, because the first stages of these diseases are very similar, so that the recognition of them is not easy except for the practiced physician. It must not be thought, however, that because these are diseases of childhood and because a majority of children have them at one time or another, without great suffering and without serious after effects, they are on that account to be despised. Scarlet fever, for instance, is to-day probably the most dreaded of children's diseases, not because so many children die of it,--although the death-rate is large, about 20 per cent of the cases finally succumbing,--but because of the large number of complications and consequences which are directly due to this disease. Measles, also, though not to the same extent, is frequently followed by serious after results. In the United States, about 13,000 children die every year of measles and about half as many die of scarlet fever. It is a significant fact that the death-rate is much higher among younger children, so that if, by carefully keeping children from the possibility of infection, the disease can be postponed until they are well along in years, the danger of fatal termination is much reduced. The following table, for instance, shows the number of deaths from measles and scarlet fever at different ages, and it is very evident from this table that if the former disease is contracted by a child under five years old, the danger of death is four times as great as if it were postponed until the child were ten years old:-- TABLE XIX. TABLE SHOWING DEATHS AND PERCENTAGES FROM MEASLES AND SCARLET FEVER FOR DIFFERENT AGES IN UNITED STATES REGISTRATION AREA FOR 1907