Eventually, it was determined that the substance emitted by the testicles is testosterone. Voronoff expected that this new discovery would prove his theories. Testosterone would be injected into animals and they would grow young, strong, and virile. Experiments were performed, and this was not the case. Besides an increase in some secondary sexual characteristics, testosterone injections did little. Testosterone did not prolong life, as Voronoff expected. In the 1940s, Kenneth Walker, an eminent British surgeon, dismissed Voronoff's treatment as "no better than the methods of witches and magicians."