There are two aspects to the problem of describing the homeopathic effect in physical terms: the nature of the therapeutic agent, and the system on which it acts. The latter can be considered as a network, which provides a conceptual framework that throws new light on long-standing questions, based on generic results such as the enhanced susceptibility of networks near critical states. It suggests a characterisation of health and disease in terms of distance from a critical state. The Internet provides a concrete analogy. This predicts a limiting condition on the acceptable loss of highly connected nodes in the system, and suggests a procedure to measure its connectivity and related parameters.