Is the Local Vasodilatation after Different Tissue Injuries Referable to a Single Cause?

Experiment shows that the vascular contraction responsible for Bier's spotting prevails over the local vasodilatation due to mechanical injury of the skin, and causes the local reddening to blanch. It is without effect, however, upon the local vasodilatation caused by histamine pricked into the skin. The results raise doubts concerning the validity of the hypothesis referring all local vasodilatations to the action of a single chemical substance or set of substances ("H substance"), liberated within the tissues.