In spite of the fact that Helmholtz made a decisive contribution to the first principle of thermodynamics by his Erhaltung der Kraft of 1847 he did not participate actively in the following debates about the nature of heat. Probably he was cautious in some way as he did not yet belong to the community of university physicists. His research concentrated on physiology at that time. On the other hand he was rather influential by his public speeches and his comprehensive reviews on problems of heat even without further publications. Insofar the discussion of Helmholtz's activities on heat of the time before he became chairholder of physics in 1871 will help to understand his special relation to physics in this early period.