It is generally believed that there is a reduction in the volume of the circulating blood in all types of shock. In instances of shock without hemorrhage, the diminution of the blood volume is attributed to a passage of fluid from the blood into the tissues. The cause of the increased capillary permeability is as yet unknown, but most of the recent experimental work has seemed to support the view that it is the result of the presence of some toxic substance. Cannon believed that most of the harmful results of diminution in the blood volume are due to the reduction of the oxygen supply of the tissues. If the reduction in the oxygen supply of the tissues is an important factor in the pathogenesis of shock, then it would seem that information of value might be obtained from a study of the oxygen content of venous blood in various