afford a theoretical explanation of the clinical observation that blood is more effective than gum. Its use will tend to establish more quickly the “virtuous circle” following increased volume, and so undo the “vicious circle” due to insufficient volume. It has been questioned whether the corpuscles of transfused blood really do play an active part in the economy of their new host, or whether their new environment may not quickly render them effete. This has been answered by the exceedingly interesting and ingenious series of experiments carried out by Winifred Ashby. She has transfused blood of a known group (see Chapter IV) into an individual of a different, but compatible group, and then shown that it is possible by selective agglutination with a suitable serum to demonstrate the presence in the blood of the two kinds of corpuscles side by side. In this way she has shown that transfused corpuscles are still present in the circulation and of normal appearance thirty days after they were introduced. It is therefore justifiable to make the inference that transfused corpuscles can for some little time carry out their normal function. If it be true that their presence is an advantage in the treatment of deficient blood volume, it may also be conjectured that their presence is likely to be of greater importance in treating hæmorrhage than it is in the treatment of pure shock, for in the latter condition all the original corpuscles are still present in the body, while in the former they are not. I should sum up the discussion of the relative merits of blood and gum by saying that on the grounds of experiment and clinical experience I believe blood to be the more efficient of the two, particularly in the most serious cases. Every patient who needs it should therefore have the advantages conferred by blood transfusion if it can be done. If it cannot, then gum and saline is much the most satisfactory substitute that is at present known.