Using a grant he acquired through his connection with the Rockefeller Institute Holt surveyed the quality of milk in the tenement districts and subsequently proved that a large proportion of infant fatalities were due to excessively high bacterial counts.

[4] In 1887, a hospital designated solely for children became a reality when five determined women purchased a brownstone house at the corner of Lexington Avenue and 55th Street, near the site of Bloomingdale's today.

At his first rounds examining the patients, he noted with interest, the practice of the nurses there in maintaining a clipboard at the bedside (cribside) upon which important clinical information was being kept.

His book included a schedule of activities (such as toilet training) to be learned at specific ages, and meals to at regular hours to "prevent disease".

In 1900, the Rockefeller family funded the construction of a new Babies' Hospital at the same site, a 10-story state-of-the-art building that still stands to this day.

[4] As president of the American Association for the Study and Prevention of Infant Mortality (AASPIM), Holt promoted reproduction control by society as a means of eugenics.

The race is to be most effectively improved by preventing marriage and reproduction by the unfit, among whom we would class the diseased, the degenerate, the defective, and the criminal.

[3] In 1923, despite his old age, the Rockefeller Institute called on him to lecture at Peking Union Medical College for their winter term.