After the foundation of the new mechanics by Galileo the character of biological investigations changed and no wonder that it was precisely the XVIIth century which gave the first mechanical theories of life in the modern sense. This paper offers some critical remarks on Cartesian hypothesis of the beast-machine, Harvey's discovery of blood circulation, Santorio's experiments on metabolism, Borelli's application of mathematics and mechanical principles to the study of muscular work and, finally, Leibniz' and Hoffmann's dynamic views