Physico-chemical sciences are dominated by the deterministic interpretation. Scientific medicine has generally been assigned to the area of functional biology and thence to the physico-chemical sciences. In as much as diseases are alterations of physiological processes, they share the ontological status of the latter. However, many diseases cannot be accommodated within a deterministic interpretation. First, many diseases are initiated by errors in transmission of information and followed by natural selection. These diseases, such as tumoural transformations and autoimmune processes, behave as (...) evolutionary processes. Second, physiological processes do not cause irreversible changes while diseases may do so when not followed by restitutio ad integrum. The tendency of living organisms to maintain stationary states of great stability and minimum energy dissipation is largely due to intermolecular forces-stabilized structures, the information for which is selected during phylogenesis and decodified during ontogenesis. Diseases cause alterations of the biological structures, thereby shifting living organisms toward stationary states of lower stability and increased dissipation. The shift, reversible or irreversible, to less stable and efficient stationary states is a common thermodynamic feature of diseases. In spite of the uniqueness of their genotype, living organisms, during ontogenetic development, form spatio-temporal unrestricted classes of infinite membership. Neither stationarity nor environment-induced perturbations and consequent adaptations are sources of historicity because of the genomic programme constraint. Historicity is conferred, however, to each organism by the permanent record of such unique events as: a) the variation-selection processes occurring in the brain-mind and immunological systems; and b) irreversible alterations induced by diseases. The disease-induced changes have ontological and epistemological consequences. Since biological structures and functions are transformed into individual, historical entities, the laws of scientific medicine must be applied in clinical practice to higher levels of organization, namely to the ensembles or groups of individuals affected by the diseases. (shrink)