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 seems, therefore, that the results were probably due to another factor, as already suggested (see p. 57), which the more elaborate test failed to eliminate. The efficiency of the rapid test is therefore not invalidated. 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 hæmorrhage or shock. CHAPTER VII THE METHODS OF BLOOD TRANSFUSION Some reference has already been made in the first chapter to the rapid development in recent years of the technique of performing a blood transfusion. The earlier operators, owing to the difficulties introduced by the coagulation of blood outside the body, were constrained to make use of some method of direct transfusion, the blood flowing directly from an artery of the donor into the patient’s veins. This has now been largely replaced by one of the methods of indirect transfusion, the blood being withdrawn from the donor into a vessel in which clotting is delayed or prevented, and then injected or allowed to run into the patient’s circulation.