Haber (2004) stated that "Despite increasing doubts about the efﬁcacy of his operation, he continued to perform both human and animal operations to popular acclaim." In 2005, Kahn stated that the work Voronoff and others in the 1920s and 1930s was the basis for rejuvenation therapy, but that the therapies developed then "received widespread attention (including ridicule) in the popular press, were spread rapidly by practitioners of questionable training and ethical motivation, and ﬁnally and relatively quickly disappeared from common use".