The semeiological nature of the clinical features described by M. Raynaud have been the subject of continuous discussion since 1862. This "phenomenon" is actually a syndrome, is histo-angeic and purely microvascular, is of acral topography, and implies a predisposition: that of a particular reaction to cold. Distal irrigation and the structure and function of glomic anastomoses show certain particular features. The "phenomenon" is a microrheological storm.