Theories on the nature of living beings have been present in our culture since the beginnings of science and philosophy in ancient Greece. The two major theoretical approaches to living beings, philosophical mechanism and Aristotelian realism, appear today with renewed force in almost every confrontation concerning the theoretical considerations of life. In recent times a strong and prolific school of thought has risen, headed by the Chilean neurobiologist Humberto Maturana. This author and his school have developed a complex and articulated theoretical system beginning with a theory of living beings and a `biology of cognition,' and extending to ethical, political, and even metaphysical considerations. This work is one of the first efforts to perform a scholarly analysis of Maturana's doctrines on living beings, starting with the analysis of "On machines and living beings". The book's introduction is placed under scrutiny in this paper. A strongly mechanist philosophical manifesto is dogmatically stated at the beginning of a supposedly purely scientific approach. The challenges for a rational foundation of philosophical mechanism are critically highlighted and briefly discussed.