The state of each living system is a result of external forces that tend to disintegrate this system and of internal forces, that organise a given system. The system, in the result of bifurcation, creates a new trajectory, along which it moves. After the change of trajectory the system alterates to another type of stability. The sudden collapse of natural system structures is described by the catastrophe theory. This theory can be useful in interpretation of sudden and non-linear changes resulting from accumulation of slow and little changes of one or more parameters.
Catastrophes are the ways of achieving a new balance by stressed live systems.
These changes are called respectively - a disease, disturbance, calamity, disaster, and so on. A new interpretation of phenomena that proceed in living systems could be given by one of the most general concepts of nature understanding, i.e. theory of chaos. You can see the degree of complication of coacting phenomena on the image generated by computer presenting the co-operation or coexistence of 3 variables involved in the pathological process. We started to analyse some typical and the most important pathological phenomena in Eastern Europe and finished by the concept of disorganization of all living systems independently on what level of organization it occurs. It is necessary to their evolution, persistence, and survival.