The Technique of Blood Grouping and The Indications for Blood Transfusion.

Blood Grouping. It is essential that the stock agglutinating sera used are of satisfactory potency and devoid of prozone phenomenon (inhibitory action, when undiluted). Such sera should have an initial agglutinin titre of at least I in Ioo and will then remain reliable, even at room temperature, for at least six months (sera conforming to these standards are now available commercially from Messrs. Burroughs Wellcome and Company). An opal glass plate constitutes the best surface on which to carry out blood grouping. In cold weather, to minimise the possibility of minor degrees of "cold agglutination, it is wise to warm the plate by holding under the warm water tap and then wiping dry before use. A drop of each of the Group II and III* sera, contained in capillary tubes of distinctive colour, is placed on the plate in areas labelled with a grease pencil, care being taken in assigning each serum to its appropriate space. A globule of blood is obtained by needle puncture of the finger or ear lobe of the individual to be grouped and a small drop transferred to, and mixed with, each of the stock sera with a platinum loop. The amount of blood added is sufficient to colour the mixture pink, but not deep red; with the former proportions it is easier to recognize finer degrees of agglutination. The platinum loop must be heated and cooled between each addition. The circular area covered by each red cell-serum mixture should be about half-an inch in diameter. The plate is gently agitated so as to ensure adequate admixture of the red cells and sera, and, provided the latter are potent, agglutination, if it is going to occur, will show macroscopically within two minutes. The aid of a small hand lens of about x Io magnification is sometimes helpful, but the use of a microscope is not required. Re-examination of the plate after the sera and cells have been standing for some time-e.g. ten minutes-may suggest false agglutination owing to partial drying and rouleaux formation, in a previously negative result. No significance should be attached to such findings. Determination of group with a relatively fresh oxalated or citrated specimen of blood is quite satisfactory.