If the experimental evidence is a reliable guide to the vascular permeability response in inflammation, two sets of facts emerge. Firstly, the response is complex and consists of at least two phases. The early one is transient and appears irrelevant to the later, which constitutes the essential part of the response. Secondly, histamine and 5-HT are the only natural mediators that have been firmly identified, but their role is confined to the early and minor events.
This information has been established largely by forsaking the gross procedures formerly used to induce experimental inflammation. If further progress is to be achieved, it is more likely to come by studying the reactions elicited by mild stimuli in animals that are not assaulted by overwhelming doses of drugs.