He specialized in Jewish demography[2] and economic history,[3] and wrote in Yiddish, German, and English.
During the February Revolution in Russia he helped found the United Jewish Socialist Party and served on the editorial board of Naye Tsayt, its official journal.
There he was a correspondent for the New York Yiddish daily Forverts, a role he continued for more than 40 years.
And Lestschinsky jacob sent a dispatch to Forward which was published in the New York Times on March 26, 1933; in it he said: "The Hitler regime flames up with anger because it has been compelled through fear of public foreign opinion to forego a mass slaughter of Jews.
[4] He was a founding member of YIVO (Institute for Jewish Research) in Vilna (then in Poland), starting its Section for Economics and Statistics.