Jung had been familiar with alchemical texts from around 1910. In 1912, Theodore Flournoy had presented a psychological interpretation of alchemy in his lectures at the University of Geneva and, in 1914, Herbert Silber published an extensive work on the subject. The first chapters of Mysterium Coniunctionis are descriptive details and lengthy amplifications of numerous images of "the opposites" that are to be reconciled and joined together to create the self. Jung described the achievement of the unio mentalis as establishing a spiritual counter-position to the purely natural. In personal development, Jung described the unio mentalis as the stage when one has achieved knowledge and insight about one's unconscious, primarily about the shadow. However, this knowledge has reached only a theoretical stage and, according to Jung, requires a further stage, that the knowledge gained from achieving the unio mentalis is applied to actual, embodied life.