[The neurological and embryological studies of Santiago Ramon y Cajal].

The neurological and embryological work of Santiago Ramon y Cajal appeared in three stages: a) Between 1888 and 1893 observations on the development of neuron prolongations led to the observation of the growth cone and formulation of the neurotropic hypothesis. b) Between 1905 and 1908 the study of regenerative phenomena in nerves and nervours centers presented a large body of evidence consistent with the neurotropic hypothesis. c)Between 1910 and 1914 an experimental program was undertaken to test the neurotropic hypothesis; this program led to conclusions on the origin and chemical nature of the growth stimulating factor. These contributions initiated an important line of research that none of Ramon y Cajal's disciples could continue. In the nineteen fifties a group of researchers from three disciplines (biochemistry, embryology and neurohistology) discovered the existence of nerve growth factor (NGF), thus initiating a fertile new field of knowledge in cell biology.