Blood volume and circulation time in children.

By means of these two methods there is determined only that portion of the total blood volume which is in rapid circulation, the other part, the so-called stored or depot blood, which is moving slowly or is almost stationary, being neglected. The organs which may act as blood depots are the spleen, the liver, the intestines, the sub-papillary plexus of the skin and possibly the muscles. The greater part of the capillary system of these organs is quite extensive enough to supply stored-up blood as and when required to the more rapid circulation or alternatively, withdraw rapidly circulating blood and store it. This action is regulated by the autonomic nervous system. The circulating blood volume as de-termined by the above methods is not absolutely fixed in quantity but chatnges within wide limits, according to the physiological or pathological conditions under which it is measured. At the same time the stored-up blood varies in the contrary direction, provided that the total volume of blood is not affected by external losses. In the latter case, the organs containing the stored-up blood strive to make good the loss of circulating blood by sending blood into the circulatory system.