[Deterministic chaos in biology]

Higher physiological organisms are characterised by a complex interaction of multiple control systems. This interaction permits man to adapt those unexpected demands given by experimental changes. The idea of complexity results basically from the non linearity of dynamic systems that are correlated to each other through feedback cycles. These systems fluctuate in an apparent chaos. The improvidence and the non uniformity of biological systems are basic qualities that define the state of health. It is anyhow possible to discriminate in them a certain repeatability of interaction that succeeded each other; this repeatability makes the system fit for a fractal interpretation.