(en) Simon Louvish, Monkey Business : The Lives and Legends of The Marx Brothers, New York, NY, St. Martin's Press, , 1re éd., 471 p. (ISBN978-0-312-25292-2, LCCN2001270712), p. 10–11 "Family lore told privately of the firstborn son, Manny, born in 1886 but surviving for only three months, and carried off by tuberculosis. Even some members of the Marx family wondered if he were pure myth. But Manfred can be verified. A death certificate of the Borough of Manhattan reveals the he died, aged seven months, on 17 July 1886, of 'entero-colitis,' with 'asthenia' contributing, i.e. probably a victim of influenza. He is buried at New York's Washington Cemetery, beside his grandmother, Fanny Schoenberg, who died on 10 April 1901."
Mikael Uhlin's Marxology, "Animal Crackers" : "It was almost filmed by United Artists in 1928, but luckily it wasn't, because how would a silent movie of this musical have been? Instead, Paramount filmed it the year after as one of the first talkies. It reportedly ran as much as 140 minutes at a preview but was cut back to 96 minutes for release." « Marxology » (consulté le )
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(en) « Samuel Marx, Father of Four Marx Brothers of Stage and Screen Fame », New York Times, (lire en ligne, consulté le )
