THE ROLE Of cardiac output, blood volume, and peripheral resistance in haemorrhagic shock have been well studied, but changes in the interstitial fluid which occupies 15 per cent of the body weight have received little attention. This is remarkable in view of the fact that this huge pool of water, electrolytes, and metabolic components appears now to be a functional mobile fluid which responds very quickly to changes in environment. Though there are many methods, both direct and indirect, for measuring intravascular fluid, which represents only one-fourth of the total extracellular fluid, no method was available for the measurement of extravascular, extracellular fluid for a long time, since it is relatively inaccessible for analysis. Recently, indirect methods of measuring entire extracellular fluid volume have been attempted using sucrose, inulin, and radioactive labelled sulphur, a-:~ Extracellular fluid plays an important role in the pathophysiology of haemorrhagic shock. One of the constant phenomena associated with the development of irreversib]e haemorrhagic shock in animals is the loss of extraceUular fluid into the lumen and wall of the bowel. Correlated with this observation is the occurrance of haemoconcentration in animals that do not survive, eveaa though shed blood is returned. 4 This report describes an experimental study undertaken to evaluate the comparative usefulness of blood, lactated Ringer's solution, dextran, and low-molecular-weight dextran in dogs, after subjecting them to rapid removal of 50 per cent of their blood volume:
METHODExperiments were conducted in 32 healthy adult mongrel dogs of either sex, weighing 8 to 20 kg. No premedication was given. They were induced intravenously with 20 mg of thiopentone per kg body weight, and anaesthesia was maintained with a gas mixture of oxygen 30 per cent and nitrous oxide 70 per cent, allowing the animals to breathe spontaneously through a Magill's semiclosed circuit, with the expiratory valve open. Traces of ether were added initially, in the prehaemorrhagic stage of the experiment only, to produce a tranquil state.
