1. Intravascular agglutination can occur, and is the probable cause of occasional untoward symptoms, or even death, following transfusion of agglutinative blood. In the majority of cases, however, it does not occur, or if it does, it causes no symptoms. This is dependent on the influence of three factors: (1) concentration of the agglutinin; (2) absorption of the agglutinin by an excess of agglutinable cells; (3) interference with agglutination by an excess of non-agglutinable cells, so that when clumps occur they are microscopic in size.
2. If, for a given transfusion, a non-agglutinative donor, i. e., a donor whose blood is of the same agglutinative class as the patient's, can not be obtained, then it is safer to use a person whose serum is agglutinative toward the patient's cells than one whose cells are agglutinated by the patient's serum.
3. Tests for agglutination, as well as for hemolysis, ought to be made before transfusion. When time does not permit this, one has to weigh the possible dangers of agglutination or hemolysis against the dangers of letting the patient go without transfusion.
4. Agglutinable cells when transfused are taken up by the phagocytes in the patient's blood; and, for this reason) the transfusion of agglutinable blood, even when no accident happens, can be expected to do little permanent good.