In a previous communication we1reported on the incidence of morbidity and mortality among 20,000 artificially and breast fed infants and the conditions under which these statistics were obtained. A commenton that paper has led us to insist on certain points. In the first place, these children were in an environment in which they were peculiarly subjected to the chance of infection; secondly, the group of partially breast fed includes two classes of children: (1) those who were entirely breast fed for a time and then had to be weaned and (2) those whose breast feeding had been complemented. The artificially fed group consisted only of those children who had been artificially fed from the first. We took only those cases which had been under our care for nine months with the exception of those children who were under our care continuously until the time of death.