Ernst Wilhelm Ritter von Brücke was the son of Johann Gottfried Brücke, a painter of portraits. He was a very famous German physiologist and doctor who was born born June 6, 1819 in Berlin, Germany and who died January 7, 1892, Vienna, Austria. He was to have a profound influence on Freud, leading the latter to abandon his earlier enthusiasm for Brentano and for pursuing studies in philosophy at a later date. Now Freud was transfixed by the modern teachings of the great physiologist Brücke who has lent his name to many important discoveries among which we may name (i) the Bezold-Brücke phenomenon, that is a change to the perception of colours under the effects of increased light intensity and (ii) the Brücke's muscle which refers to the longitudinal fibres of the ciliary muscle. It is beyond the scope of these preliminary notes to say much more on this great scientist's anatomical discoveries. What we are about is his influence on our man Freud.
A note on Vitalism:
Under this heading one could in fact group a whole miscellany of beliefs which were united by the strong conviction that living organisms are not to be explained in terms of their material composition or their physico-chemical performances or actions and re-actions. Such beliefs were to be found in the writings of Hans Driesch (1867-1941) and Henri Bergson (1859-1941). These scholars argued that living things are animated by a vital principle such as entelechy (Driesch's term) or an élan vital or life force (Bergson's terminology). I advert to vitalism here because it is usually contrasted with mechanism or even materialism - a whole system of beliefs to which modern biology and indeed medicine owe all their great triumphs.
Raymond E. Fancher in his magisterial Pioneers of Psychology ( W.W. Norton & Company, 1999) has this to say on Ernst Brücke's influence on Freud:
[He] became for Freud the figure "who carried more weight with me than anyone else in my whole life." Together with Hermann Helmholtz, Emile du Bois-Reymond, and other students of Johannes Muller, Brucke had been a founder of the enormously productive "new physiology" which rejected vitalism and sought mechanistic explanations for all organic phenomena... Tremendously impressed by Brucke and his mechanistic physiology, Freud began devoting all his spare time to volunteer research... he worked well, and by 1880 had published four articles on neuroanatomy, and looked forward to a career in that field.
As a result Freud remained a determinist or reductionist or mechanist throughout his life, believing that all vital phenomena like thoughts, feelings or phantasies are rigidly determined by cause and effect.
Above I have uploaded an image of Ernst Brucke