THE physiology of blood groups having been examined, the principles governing the choice of a blood donor can be more readily understood. It is evident that this choice is determined largely by blood groups, and in the present chapter therefore the clinical methods of testing for the groups will be described.

Before, however, the bloods can be tested, a willing donor must be found, and this is not always an easy matter. During the war, even when transfusion was being practised on a large scale, there was never any difficulty in finding volunteers among the men that were more lightly wounded. In addition tothe genuine and ready response which many men would make at once to a call for help in a matter of life and death, there was the glamour of novelty, and the feeling of satisfaction following an act of conscious heroism ~for such the sacrifice of blood was held to be, the days having long been forgotten when as much blood was " let " in the treatment of almost any ailment. In the Expeditionary Force, too, the unofficial reward of a fortnight's, leave in England proved a potent inducement, and the rejection of A volunteer on the ground of incompatibility was regarded almost as an injustice or as a reflection upon the physical condition of the candidate. In civilian life, however, such inducements cannot be held out, and it will be found that many a man " does not like the idea " of parting with a pint of blood, even though the sacrifice may sai,e another's life. Often, however, a near relative of the patient may happen to be willing and suitable, or, failing this, in a hospital ward there will usually be some young man who has been admitted for a slight operation, such as the radical cure of a hernia, and will accede to a request for blood if the procedure, its object, and its harmlessness to himself be briefly explained. Notoriety is fortunately seldom a motive for volunteering, and though paragraphs have occasionally appeared in the daily press with headings such as "Police Inspector's Sacrifice," this has probably not been done by the donor's own wish. It is, after all, natural that to the mind of a layman the giving to another of so personal a possession as his blood should seem to be an act of heroism, and it is also natural that occasionally a man should feel some repugnance to taking part in a strange performance which he but dimly understands. To the young, on the other hand, the procedure may appeal by its faint flavour of adventure.

Occasionally during the last two years advertisements for blood donors have appeared in newspapers, probably not in vain. If the demand for blood donors becomes greater than it has been as yet, it will certainly result in the creation of a class of " professional blood donors," who already exist in some numbers in the United States of America, where blood transfusion is a more widely recognized form of therapeutics than it is in this country. These professionals have even formed a Trade Union, so that as high a fee as possible may be obtained from those who need their blood. Apart from this, some of the advantages of having these professionals available have already been explained in the chapter on the dangers of blood transfusion. It is evident that certain sources of danger can be eliminated in advance, and in an emergency it is obviously better to have donors of known groups available, so that no time is lost in testing the prospective donors of whom several in succession may 4be found unsuitable. Probably it will be easier for practitioners to arrange for such professionals to be available at the shortest notice than for necessary arrangements to be made in a hospital. Even in large institutions it is usually difficult for any of the men employed in them to be spared from their work for twenty-four hours, so that, although suitable men of' known groups are always within call, it may be impossible to use them. This, however, is not the place to discuss the organization that is necessary to make a 'blood transfusion a really efficient form of emergency treatment in a hospital. It may merely be observed that in every hospital it should be possible to give a blood transfusion to a patient suffering from urgent haemorrhage within fifteen minutes of his arrival on the premises.

Whether the donor be a "professional" or an "amateur," it may be useful to mention a few points to be observed in choosing him. , There can be no doubt that the most satisfactory individuals for the purpose are young men between the ages of eighteen and twenty five. The younger the donor, the less likely is he to be suffering from certain of the diseases mentioned in the chapter on the dangers, the less will be the immediate effect of the withdrawal of circulating fluid, and the more quickly will he recuperate from the loss of blood.

It must not be supposed, however, that the withdrawal of even 1,000 cc. of blood will usuallyhave an appreciable effect upon a healthy man. It is impossible to predict from the donor's appearance what immediate effect the loss of blood will have upon him. It sometimes happens that the most robust-looking individual becomes faint after losing a few hundred cubic centimetres, whereas another, to all appearances pallid and much less satisfactory, will not evince the slightest discomfort from the loss of 750 cc. or even more. Normally a man should be able, by his physiological mechanisms, to compensate reflexly and at once for the removal of this amount of fluid from his circulation. In any case, the worst effect that is seen in a well-chosen donor is a transient faintness ; it is usually wise to keep him on his back for two or three hours after the operation, and he should not, if it can be avoided, return to his work on the same day. During the late war a medical officer of my own acquaintance gave 750 cc. of blood for a severely wounded friend and continued his arduous duties as Surgical Specialist in a Casualty Clearing Station immediately afterwards. In this case, however, the donor was solely responsible for his own welfare; usually this responsibility rests upon another, and greater care must be exercised. The effect, indeed, of a transfusion upon the donor seems to depend more upon psychological than upon physiological factors. A nervous and excitable donor is more likely to suffer than one who approaches the operation without apprehension. This is another point in favour of employing a professional donor, who soon becomes familiar with the whole procedure and will lose all symptoms of fear.

The same considerations may be applied to the use of women as blood donors. In them the spirit of self-sacrifice is commonly more highly developed than it is in men, and some of the most eager donors will be found among them. The disability of nervousness will, however, occur more often in women, and another consideration of importance is that the veins of a woman are usually much less easily accessible than those of a man. Not only is the abundant subcutaneous fat an impediment in women, but usually the superficial veins are all of small size. The method of choice for performing a blood transfusion will be presently described, and it will then be seen that the operation is easier and that much less damage is inflicted on the donor if a large superficial vein can be tapped. In women this. will very often be difficult or even impossible. In general, therefore, it may be stated that the use of women as blood donors is to be avoided. The fallacies concerning the indiscriminate transfusion of an infant with its mother's blood and of any patient with fhe blood of a near relation have already been explained.


Reference to the table of blood reactions given will show that in order to discover the blood group of any individual it is only necessary to test his corpuscles against the serum of Groups II and III. These reactions may be recapitulated as follows

(i) If he be Group I, his corpuscles will be agglutinated by the serum of Groups II and III.

(ii) If he be Group 11, his corpuscles will be agglutinated by the serum of Group III only.

(iii) If he be Group III, his corpuscles will be agglutinated by the serum of Group II only.

(iv) If he be Group IV, his corpuscles will be agglutinated by neither serum.

Only the serum, therefore, collected from people known to belong to Groups II and III need be kept in stock. This can generally be obtained from the Lister Institute, and if kept sterile will retain its agglutinating properties for some months. but under no circumstances should serum more than slliLonths old be used, since the consequences of a failure to agglutinate may be very serious. Nevertheless, the agglutinins contained in serum are very resistant to physical and chemical changes in their environment. Dried serum has been successfully used for testing purposes, and Culpepper has shown that the reactions are not interfered with by cold or by heat until actual coagulation of the serum takes place. Bacterial contamination does not affect the reactions so that the serum is still active even when putrid. Various methods have been used for preserving.the serum. Its properties are not affected by the addition of dilute cresol (1: 250) or of chloroform.

In the absence of any stock sera, the agglutinating test may be applied directly. A few cubic centimetres of blood are taken from the patient,. and the serum as soon as it has separated is tested against the corpuscles of the prospective donor. If agglutination occurs, this donor is at once excluded. If no agglutination occurs, he is either of the same group as the patient or belongs to a compatible group. Supposing that a donor actually of the same group as the patient is wanted, then the reverse test must be performed in addition, that is to say, the corpuscles of the patient must be tested against the scrum of the donor. If both tests are negative, then donor and patient are proved to be of the same group. The method of direct test cannot be applied in an emergency owing to the loss of time involved ; it is better, therefore, that anyone who intends to be ready to perform a blood transfusion should always have scrum of Groups II and III immediately available.

The collection of stock sera is not a matter of any difficulty. strietaseptieprecautions 20 cc. of blood are withdrawn in a syringe from persons known to belong to Groups II and III; the bloods are put into a sterile testtube and allowed to clot. As soon as the serum has separated it is drawn up into sterile glass bulbs of suitable capacity, which are sealed off at each end. The most convenient form of storage for actual use is a capillary glass tube sealed at each end. Each tube may be made to hold a single drop, which is the amount used for a test. There is then no wastage of serum, and no chance of contaminating the remaining stock. When the blood has been withdrawn and has clotted, the complete settling of the corpuscles can be hastened by the use of the centrifuge. If the serum be left in contact with the corpuscles for more than twelve hours, some auto-haemolysis may take place, so that the serum will become tinged with haemoglobin. It is exceedingly important that the two stock sera should not become confused, and this may easily happen unless each tube has some distinguishing mark.

The methods of testing for blood groups have been simplified by successive observers since the existence of the groups was first demonstrated in 1907. Moss used an elaborate technique such as was essential for putting a new discovery upon a secure scientific basis. In order to obtain a suspension of corpuscles, blood was drawn into a syringe containing a solution of sodium citrate to prevent clotting. The corpuscles were collected by means of the centrifuge, and were thoroughly washed twice in normal saline solution so that they were finally collected free from serum and from citrate. Serum was collected in the manner already described. A series of small tubes was then filled with equal quantities of serum and the suspension of corpuscles, and was incubated for two hours at 37.5degrees C. At the end of this time observations were made and again after the tubes had stood for twelve hours in an ice chest. Varying degrees of agglutination and hxmolysis were then accurately recorded, and far-reaching results were obtained.

Later workers had the advantage of using stock sera belonging to known groups, so that the number of observations to be made was very greatly reduced. Brem intrGduced in 1916 a method of testing in which he mixed the serum and suspension of washed corpuscles in verysmall quantities on a coverslip, which was inverted over an ordinary cell slide rimmed with petroleum jelly. The results could then be observed macroscopically or under the microscope, and the presence or absence of agglutination could he determined within fifteen minutes. The detection of hxmolysis by the hanging drop method requires that the cells should be incubated and observed at intervals for several hours, but it is not always easy to see the disintegrated corpuscles unless the process has taken place extensively. The diagram on p. 105 gives in a tabulated form some idea of the appearances presented by the corpuscles of the different groups when mixed with the stock,sera and observed in a hanging drop under a microscope. Agglutination must he distinguished from the formation of rouleaux, which may be seen in. any of the mixtures.

For scientific purposes these very careful tests are necessary, but it seems to be clear that for clinical purposes, a much rougher and quicker test is adequate. In the clinical determination of blood groups it is superfluous to carry the test to the point of watching for hwmolysis, for it is upon the presence of agglutinins in the serum and the corresponding agglutinnins in the corpuscles that the deterermination of the groups depends. Further, no error is introduced by neglecting the haemolysis, since it has been shown that haemolysis is invariably preceded by agglutination. It is the occurrence of agglutination therefore that is of prime clinical importance. If that is excluded, haemolysis is necessarily excluded also, and the prolonging of the test is seen to be only of academic interest. In the methods described above the corpuscles were always tested in the form of a washed suspension. This precaution was taken on the supposition that the presence of any of the serum belonging to the corpuscles might interfere with the reaction. If, however, the amount of this serum be small relatively to the amount of the test serum, then no such interference takes place.

The ordinary clinical method of testing may therefore be greatly simplified, and the one commonly used at the present time is as follows : A single drop of each of the stock sera is placed on two glass slides, or, better, side by side upon a white glazed tile or plate, the numbers of the groups. II and III, being written above the respective drops. The lobe of the ear of the person to be tested is then washed with ether and pricked with a sterile surgical needle. A small quantity of the blood which exudes is taken up on the end of a blunt metal or glass rod, and is intimately mixed with the drop of serum under the number II. The end of the rod is then carefully wiped clean, and a similar small quantity of blood is mixect with the drop of serum marked III, The amount of blood to be used should not be so great as to make the drop of too deep a colour, which may interfere with observation of the, reaction, but it should be enough to impart to it a very definite red tint. The slide or tile is then gently rocked, so that some slight movement is imparted to the drops, which are at the same time closely watched in a good light. The agglutinating reaction is readily seen with the naked eye, especially against the white background provided by the tile. If the scrum be properly active, the agglutination of the corpuscles begins to be apparent as a definite granular appearance resembling brick dust within a minute of mixing. With a little practice this appearance is easily recognized, but it must be distinguished from the appearance produced by a mechanical gravitation of the corpuscles towards the centre of the drop. If agglutination is taking place, the granulation appears simultaneously throughout the drop, and not only in the centre. With an active serum the process may proceed rapidly, so that in less than five minutes the corpuscles have been aggregated into a few irregular masses; often it stops short of this, but the drop presents, nevertheless, a coarsely granular appearance which is quite unmistakable. If no granulation can be seen at the end of five minutes, it can be assumed that the test is negative for serum of that group, and the group of the corpuscles may be deduced upon the principles already explained. The test carried out in this way is admittedly not susceptible of the same finesse as if it were done with the assistance of the hanging drop, the incubator, and the microscope ; nevertheless, my own experience in a large number of cases has shown that, clinically, this test may be relied upon, and the same view has been expressed by other writers on the subject. Very seldom is there any doubt as to the presence or absence of agglutination.

When doubt exists, it is easy to repeat the test and obtain a confirmation of the result. It may perhaps be urged that this test is quite insufficient for eliminating the slighter degrees of incompatibility which have produced serious results when the transfusion has been repeated several times. But in the cases reported, the blood that was used had not shown any agglutination even when most carefully observed under the microscope. It is, nevertheless, in the present state of knowledge, a wise, precaution to perform the direct test between patient and donor in addition to the group test when circumstances permit. It is essential when the patient is suffering from any form of blood-disease. It is unnecessary when the transfusion is to be performed as a life-saving operation in haemorrhage or shock.