11)20] on The Volume of the Blood and its Significance 49 



responsible for the toxaemia of injury. But that the agent is some- 

 thing which acts in the same way is made clear by the observations 

 that have been made on wounded men. The determinations of the 

 volume of the blood in circulation, made by N. M. Keith, may be 

 especially mentioned. Keith showed that, in severe cases, it may be 

 reduced to little more than half the normal amount, although scarcely 

 any has actually been lost by haemorrhage. The method used was 

 that of introducing into a vein a known quantity of an innocuous 

 dye which does not pass through the walls of the blood-vessels, and, 

 after a short interval, taking a sample of the blood and finding how 

 much the dye has been diluted. 



If the toxaemia is severe, a second property of the poison shows 

 itself. This is an effect on the walls of the capillaries such that they 

 allow the liquid part of the blood to escape by filtration. In this 

 way the volume of the blood is still further reduced. 



The treatment, in principal, is obvious. Restore the blood-volume. 

 It would appear that when blood has been lost it ought to be replaced 

 by blood. The case of traumatic toxaemia is not so clear at once, 

 because blood has not been actually lost, and it should be possible to 

 keep up an effective circulation by some other liquid until the poison 

 is got rid of and the pooled blood returned to circulation. In fact, 

 as experience increased, it was realised that the important matter is 

 to maintain the volume in circulation, whether by blood or other 

 solution. An innocuous fluid seemed to serve practically as well as 

 blood, and had the advantage of being always at hand and in as large 

 a quantity as required. 



As to the properties of such a solution, it was soon found that a 

 simple saline solution is very rapidly lost from the circulation and is 

 useless. It is necessary to add to it some colloid with an osmotic 

 pressure, such as gelatin or gum acacia. The colloid does not pass 

 through the walls of the blood-vessels, and its osmotic pressure 

 causes an attraction of water to balance that lost by filtration. Thus, 

 although the slow circulation incidental to a small volume of blood 

 is inadequate, this very quantity, if diluted to normal volume, is able 

 to serve effectively. Comparing the oxygen carried by red corpuscles 

 to railway passengers, it will be realised that if we have a limited 

 number of trains, we can carry more passengers in a given time if the 

 velocity of the trains is increased. Animal experiments made by 

 Gasser showed that this is actually the case with the blood. After a 

 loss of blood the injection of gum-saline might even raise the supply 

 of blood-corpuscles to a level beyond what it was before the haemor- 

 rhage. 



The general conclusion is that the volume of the liquid in 

 circulation must be kept up to its normal value, whatever this liquid 

 may be. Of course, the number of red corpuscles cannot be allowed 

 to fall below some particular value, and it has been found that about 

 one-quarter of the normal quantity is the lowest compatible with life. 



Vol. XXIII. (No. 114) e 



