He was a key figure in the movement to improve child healthcare and welfare in the United States[2] and opened the first children's clinic in the country.

[4] Born in Hartum (now a district of Hille), Westphalia, he was the son of a poor Jewish shopkeeper and his wife,[5] who educated him at great sacrifice.

[2] He remained in contact with Marx and Engels and in 1857 Jacobi was involved in founding the New York Communist Club.

[6] In the summer of 1918, a house fire destroyed the manuscript of his autobiography, and other personal papers at his Lake George home.

Jacobi contributed chapters on the care and nutrition of children, diphtheria, and dysentery to Gerhardt's Handbuch der Kinderkrankheiten (Tübingen, 1877), and on diphtheria, rachitis, and laryngitis to Pepper's System of Practical Medicine (Philadelphia), and has published lectures and reports on midwifery and female and infantile disease, and a number of articles in medical journals.

His Sarcoma of the Kidney in the Fœtus and Infant is printed in the Transactions of the International Medical Congress in Copenhagen.