Ricker's Law

RICKER'S LAW of stages (Stufengesetz) concerns the relationship between the state of vasomotor nerves and the strength of their stimulation. According to Ricker, weak stimuli excite only dilators, causing dilation of vessels and acceleration of blood flow, which increases blood supply to the organ. Stronger stimuli excite constrictors, causing narrowing of the vascular bed and slowing of blood flow in capillaries and veins. With even stronger stimulation of vasomotor nerves, closure of small arteries and capillaries occurs, stopping the flow of venous blood. Finally, the strongest stimuli lead to the extinction of the action of constrictors and strong stimulation of dilators, which later also become paralyzed. Severe dilation of vessels occurs with acceleration of blood flow, which soon then slows down and completely stops, since the feeding artery experiences narrowing at this time. The last mechanism with higher degrees of stimulation underlies the so-called stasis. The initial degrees of stimulation were experimentally achieved by irrigating the rabbit's mesentery with a physiol. solution of NaCl at 43°; the following degrees with the same solution at 47° and the highest degree was obtained with a solution temperature above 50°. Ricker's Law has not gained universal acceptance. In particular, it was pointed out that not only the strength of the stimulus but also the nature of the stimulus is important, that the specified order of effects may be disrupted, and that for different tissues this order may change. Despite the objections made (Tannenberg, Fischer-Wasels, Groll), the work of Ricker and his school proved to be an important step forward in the study of such seemingly elementary pathological processes as hyperemia, ischemia, stasis, and bleeding. These work were also a step forward in that they introduced elements of connection into these processes, which are qualitatively distinctive, demonstrating transitions of one phenomenon into another, sometimes opposite, when only the quantitative side of the stimulation itself changes.