Organon §63

Each potence that impinges upon the life force produces an initial action which elicits an automatic reaction from the life force, termed an after-action or counter-action.

 Each life-impinging potence, each medicine, alters the tuning of the life force more or less and arouses a certain alteration of a person’s condition for a longer or shorter time. This is termed the initial action. While the initial action is a product of both the medicinal energy and the life force, it belongs more to the impinging potence [of the medicine]. Our life force strives to oppose this impinging action with its own energy. This back-action belongs to our sustentive power of life and is an automatic function of it, called the after-action or counter-action.