The experiments carried out by the authors have demonstrated the arrangement of muscular elements within the capillary bed of the mesentery in the dog and rat, which, it is suggested, are capable of controlling the rate and flow of blood through the part.

Briefly, the capillary bed is formed as follows. Apart from the usual short arterio-venous anastomoses, longer capillary-like central channels pass from arteriole to venule. The proximal portion of this channel is known as the metarteriole. The true capillaries arise as loops from this central channel and the origin of the capillary loop is known as the pre-capillary sphincter. Muscular elements in the capillary bed proper are limited to the metarteriole and precapillary sphincters and it is the recurrent vasomotion of these, vessels which controls the rate of blood flow in this area. The action of epinephrine and histamine upon this circulation is described.-C. W. OTTAWAY.