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Irritability, loosely defined as the capacity to respond to stimulus, is considered by biologists as a condition of life itself.12,24,29 The founder of the doctrine of irritability of life substance, as far as we have been able to determine, was Francis Glisson,13 although John Brown of Edinburgh is regarded as the originator of the universal irritability concept (Elementa Medicinae, ).28
From an infracellular point of view, irritability may be related to an electron transformation from a state of “singlet excitation” to that of a “triplet state” (referring to the single as opposed to triple spectrum image). With this transformation, the electron remains trapped in an excited (“irritable”) triplet state. Ultimately, perhaps, the energetics of the living world consist of two parts only—photosynthesis and its reversal (Szent-Gyorgyi).26 Triplet states seem to be the main instruments of energy transmission, namely conversion of (E), bound (potential) energy, into E*, free (kinetic) energy. At this level, irritability may be defined as the readiness for conversion of potential into kinetic energy. Szent-Gyorgyi furthermore points out that biological reactions are, thermodynamically, “downhill” reactions, going with a decrease of free energy, so that, paradoxically, an impaired energy supply causes increased activity. At a different level of consideration, Wald30 has demonstrated that nutritional (energy) lack resulted in hyperactivity (irritability). He cited the migration of lemmings as a larger, ecological example of this phenomenon (Heape).15
At a cellular level, the membrane, distinguishing between outer