104 



DISCOVERY 



or delayed. If, therefore, the blood be allowed to run 

 into a vessel coated on its inner surface with a thin 

 layer of wax, and then be immediately run into the 

 recipient's veins, a measured quantity of blood can be 

 transferred with comparative case. This method is 

 still used at the present time, but it presents some 

 technical difficulties, and even in practised hands is 

 not absolutely certain of success. The last and greatest 

 advance was made in 1913, when it was discovered in 

 an American laboratory that sodium citrate, a salt 

 of the acid present in lemons and other fruits, will 

 combine \vith the calcium of the blood in such a way 

 as to render it inert. Sodium citrate, if injected into 

 the circulation in some quantity, has a very poisonous 

 effect ; but the amount of it that is necessary to 

 combine with the blood calcium is so small that the 

 mi.xture of blood and citrate solution is as beneficial 

 to the recipient as if pure blood were given. Clotting 

 is by this means entirely prevented, and the whole 

 process of transfusion is rendered both simple and 

 certain of success. 



There still existed, however, a certain danger in blood 

 transfusion, for it sometimes occurred that the re- 

 cipient, so far from benefiting by the transfusion, 

 sudddenly and unaccountably died ; it was evident 

 that some unknown quality in the blood remained yet 

 to be discovered. These fatalities found their ex- 

 planation, about the same time that the citrate method 

 was introduced, in the discovery by another American 

 observer that certain individual peculiarities existed in 

 the bloods of different people. Half the volume of the 

 blood is made up of large numbers of "corpuscles," 

 each a minute disc, slightly concave on both sides and 

 only seven-thousandths of a millimetre in diameter. 

 They contain in their substance the red pigment, 

 haemoglobin, to which the colour of the blood is due, 

 and by virtue of this substance they have the power 

 of combining with the oxygen of the air, which they 

 pick up in the lungs and convey through the circulatory 

 system to the various parts of the body. Their func- 

 tion is thus indispensable for the maintenance of the 

 life of the animal which they serve. It was now dis- 

 covered that these corpuscles, which are of very deUcate 

 structure, are in some people destroj-ed by substances 

 in the fluid part of the blood of others. Although this 

 destruction would usually result only in the loss of 

 the corpuscles of the transfused blood without any harm 

 being done, yet occasionally so potent a poison was 

 produced by the change that the consequences to the 

 recipient of the blood were fatal. It was also found 

 possible to classify people into four groups which exist 

 in a given race of people in almost constant proportions. 

 Of these, one group, the smallest (i per cent.), cannot 

 give blood to anyone except to people of their own 

 group, though they can be given the blood of anyone. 



A second group, fortunately the largest (44 per cent.), 

 are able to give their blood to anyone without ill effects, 

 though they can only be given the blood of their own 

 group. The two remaining groups, of intermediate 

 frequency (15 per cent, and 40 per cent.), are mutually 

 antagonistic, though their blood can be given to mem- 

 bers of the first group mentioned and of their own 

 group. A test for these groups can be easily made 

 and is completed in a few minutes, so that it is now 

 the practice to use as blood-donors people of the second 

 group or of the same group as the recipient. The 

 danger of death from incompatibility of bloods has 

 thus been eliminated. It is believed that this grouping 

 is not dependent on any fortuitous conditions, such as 

 diseases that the individual may have suffered from, 

 but to be due to differences of a chemical nature, which 

 are inherited in a definite, though as yet undetermined, 

 manner. The blood of a baby is found to have its 

 characteristic group reaction as soon as it is bom, and 

 it does not necessarily belong to the same group as its 

 mother. 



It is difficult to find out accurately the total amount 

 of blood circulating in the body, but phj'siologists have 

 estimated it to be between seven and ten pints. It is 

 still more difficult, for obvious reasons, to find out 

 how much blood a man may lose and yet remain 

 alive ; but the body can accommodate itself by various 

 mechanisms to differences in amount %\ithin fairly wide 

 limits, and it is this power of accommodation that 

 makes it possible to take from the donor as much as 

 a pint and a half of blood not only without danger, but 

 often without any effect at all, though some donors 

 experience a transient faintness. Probably nearly half 

 the total amount of blood can be lost without neces- 

 sarily causing immediate death ; but there can be no 

 doubt that the loss of as much as three pints of blood 

 will put a severe strain on the mechanism of accom- 

 modation, and to some individuals would be extremely 

 dangerous. If a man has been sev'ereU" wounded on 

 a battle-field, his collapsed condition may have been 

 brought about by several factors besides loss of blood. 

 The wound may have given a very severe shock to 

 the whole nervous system, the man may be cold and 

 in need of food and drink, and he may in addition 

 have lost blood in any amount up to three or four 

 pints. As a result his heart may be exhausting itself 

 in an attempt to force the remaining blood round a 

 circulatory system which has become too big for it, 

 and his lungs are faihng to do their work of oxygenating 

 the blood owing to the inadequacy of the supply that 

 reaches them. The body will replace a certain amount 

 of fluid at the expense of the organs, but this amount 

 is Hmited. 



Until the methods of blood transfusion became 

 widely known, doctors sought to replace the fluid 



