+As the length of the period of suckling of the preceding child increases, there is a constant and rapid decrease in the number of children who are born at intervals of less than one year.+ If the preceding child was not breast-fed a new birth occurred before the expiration of one year in 9.6 cases out of 100. With a suckling period of one-half to three-quarters of a year of the preceding child, this figure is reduced to 1.8 per cent., and after a still longer suckling period to 1 per cent. Out of one hundred mothers who have only partly or not at all suckled the preceding child, seventy must count on a fresh birth within a period of 1-3/4 years. If the preceding child was suckled for at least 39 weeks, only thirty-eight, and with a suckling period of more than a year only twenty mothers have to reckon on a fresh birth within 1-3/4 years.
Dependence of Infant Mortality on the Duration of Breast-Feeding and the Length of Time Intervening Between Successive Births.
Figure C 64 shows the +parallelism between+ the +average length of breast-feeding and the average time between births+ within the families. A half to three-quarters of the mothers who suckled either long enough or very long show an interval between births of from 1-1/4 to 3 years, whereas of those who did not suckle at all, or only did so insufficiently, only one-third belong to this group, and figure largely in the column of lower birth intervals.
Dependence of Infant Mortality on the Average Duration of Breast-Feeding and the Average Length of Time Intervening between the Successive Births of the Children in a Family.
Figure C 65 enables us to examine into the +influence exercised by a longer or shorter interval after the preceding birth on the vitality of a child+, according as to whether the child was not breast-fed at all or only moderately or amply so. The black oblongs demonstrate that the average infant mortality falls regularly and decisively according to the length of time between the birth of the children considered and their predecessors. The average mortality of infants who are born in rapid succession--under one year, one to one and a quarter years, amounts to over 25 and to 22 per cent. respectively, whereas the average mortality of children with at least two years' interval amounts only to 11 per cent. "At the same time, however, it is observed that the influence of the length of suckling is still greater than that of the length of time elapsing between births. Even with an interval of three or more years, the mortality of children who were insufficiently or not at all breast-fed was above 20 per cent. The children who had been suckled for at least three-quarters of a year were only very slightly influenced by this factor in all groups, except that with a birth interval of less than one year, where the influence of short birth intervals is not counterbalanced even by long extended breast-feeding."