In Brazil, the years from 1870 onwards were perceived as a landmark in terms of scientific activities, both qualitatively and quantitatively. In 1883, the German-born journalist Karl Koseritz acknowledged the advance of Natural Sciences, at the Faculty of Medicine and at the National Museum, whose "great collections' would almost make him 'sign a truce" with Rio de Janeiro. He would comment about the excellence of the institutions' laboratories, where experiments on yellow fever, curare and anti-snake venom sera were developed. As an enthusiastic Darwinist, he observed that, at the Faculty of Medicine, several students interested in Natural Sciences were "the most pure Darwinists". A broad understanding of the changes taking place needs to consider some central aspects, as we will discuss in the first part of the text.