If the transfusion is being done at leisure, the donor’s blood must be tested for a positive Wassermann reaction. Even this test, however, has been known to fail, and since, in an emergency, the most careful inquiry, aided by a desire on the part of the donor to arrive at the truth, may reach an erroneous conclusion, the risk of infection with syphilis can never be completely eliminated. Since reasonable care can make the danger a remote one, it need not hinder the performance of a transfusion any more than an occasional death under anæsthesia prevents the frequent use of general anæsthetics. The mere existence of such a danger is, however, an argument in favour of the general use of the “professional blood donor,” whose Wassermann reaction, personal history, and mode of life are well known to the practitioner; the previous use of his blood on perhaps more than one occasion, if unattended by any ill results, will give an added confidence. The tragedy of such a misfortune is so great that no precaution which can possibly be taken should be regarded as absurd.
The second danger present in the inherent qualities of the donor’s blood has been already alluded to in the historical sketch of the subject. Before the existence of the “blood groups” was realized, a number of fatalities due to an unexplained cause had occurred. Even after the existence of the groups had been demonstrated, the warning that resulted was apt to be disregarded, and it was not until still further fatalities due to this incompatibility of bloods had taken place that the very important nature of the discovery came to be understood. The chances are, on the whole, that the blood of any donor chosen at random will not prove fatal to a given recipient; nevertheless, it must frequently happen that the transfusion without being fatal will be wasted, or to some degree detrimental. It is therefore evident that the existence of blood groups must be seriously regarded, and it is necessary to enter into a detailed consideration of their relations to one another and the symptoms which they may produce. In the next chapters will be found a further description of their physiology and pathology and of the methods of testing for them.
It has long been known that if the blood of one species of animal is injected into the circulation of another species, the corpuscles of the foreign blood are at once destroyed, their contained hæmoglobin being set free. This process of hæmolysis is under such circumstances rapid and complete, and hæmoglobin may appear in the urine in a short time. The precise nature of the reaction is obscure and need not be discussed here in detail. The present bearing of the phenomenon is the fact that a similar, or analogous, reaction may occur when the bloods of certain individuals are mixed with the bloods of certain others even of the same species. It was the observation of this fact that first led to the discovery of the so-called “blood groups” among human beings, and so to the partial elucidation of the cause of the previously unexplained fatalities following blood transfusion. In 1901 Landsteiner had detected the presence of hæmolysins and iso-hæmolysins in blood and classified three groups in human beings. In 1907 it was shown by Jansky that human beings may be divided into four groups, the blood of the members of each group having a certain definite relation to the blood of the other groups as determined by the manner of their interaction. The work was repeated and confirmed by Moss in 1910. The reaction takes place between the serum of one group and the corpuscles of the other groups, and is evidenced by the agglutination or hæmolysis of the corpuscles that are being acted upon. In the course of his researches Moss showed that hæmolysis, or the breaking up of the corpuscles, is always preceded by agglutination or the clumping together of the corpuscles. The process does not necessarily go as far as the destruction of the corpuscles, but may be arrested at the stage of agglutination. It may, on the other hand, be as rapid and complete as if the bloods belonged to different species, and the appearance of hæmoglobin in the urine may quickly give evidence of this.
The groups have been arbitrarily numbered, and it is now usual to refer to them by the Roman numerals I, II, III, and IV. According to the accepted convention, the reactions of these four groups are as follows:[5]
The corpuscles of Group I are agglutinated by the sera of II, III, IV. The corpuscles of Group II are agglutinated by the sera of III, IV. The corpuscles of Group III are agglutinated by the sera of II, IV. The corpuscles of Group IV are not agglutinated by any of the other groups.
On the other hand:
The serum of Group I agglutinates no other corpuscles. The serum of Group II agglutinates the corpuscles of Groups I, III. The serum of Group III agglutinates the corpuscles of Groups I, II. The serum of Group IV agglutinates the corpuscles of Groups I, II, III.
This may be represented more graphically by the following table, a + indicating agglutination, a – indicating no reaction:
| Serum | |||||
| I | II | III | IV | ||
| Corpuscles | I | – | + | + | + |
| II | – | – | + | + | |
| III | – | + | – | + | |
| IV | – | – | – | – | |
The active principle in the serum is called “agglutinin” or “hæmolysin,” according to the degree of the reaction, and the corpuscles are rendered sensitive to this by the possession of an “iso-agglutinin” or “iso-hæmolysin.” Sometimes the corpuscles are said to have “agglutinophilic” properties. It may be stated, therefore, that the serum of Group I entirely lacks agglutinins, whereas the corpuscles of Group IV lack iso-agglutinins. All these terms, like the “amboceptors,” “receptors,” and “haptophores” of Ehrlich, are used to conceal ignorance rather than as an expression of knowledge, but, until more light has been shed upon the nature of the reactions, ignorance must be abbreviated.