As we have several times insisted, the quantity of haemoglobin affords the most important measure of the severity of an anaemic condition. Those methods which neither directly nor indirectly give an indication of the amount of haemoglobin are only so far of interest that they possibly afford an elucidation of the special pathogenesis of blood diseases in particular cases. To these belong the ESTIMATION OF THE ALKALINITY OF THE BLOOD, which in spite of extended observations has not yet obtained importance in the pathology of the blood. A value to which perhaps attention will be more directed than it has up to the present time by clinicians is the RATE OF COAGULATION OF THE BLOOD, for which comparative results may be obtained by Wright's handy apparatus, the "Coagulometer." In certain conditions, particularly in acute exanthemata, and in the various forms of the haemorrhagic diathesis, the clotting time is distinctly increased, or indeed clotting may remain in abeyance. Occasionally a distinct acceleration in the clotting, compared with the normal, may be observed. Wright has further ascertained in his excellent researches, that the clotting time can be influenced by drugs: calcium chloride, carbonic acid raise, citric acid, alcohol and increased respiration diminish the clotting power of the blood. Recently Hayem has repeatedly called attention to a condition, that is probably closely connected with the coagulability of the blood. Although coagulation has set in, the separation of the SERUM FROM THE CLOT occurs only very slightly or not at all. Hayem asserts, that he has found such blood in Purpura haemorrhagica, Anaemia perniciosa protopathica, malarial cachexia: and some infectious diseases. For such observations large amounts of blood are needed, which are clinically not frequently available. Certain precautions must be observed, as has been ascertained in the preparation of diphtheria serum, so that the yield of serum may be the largest possible. Amongst these that the blood should be received in longish vessels, which must be especially carefully cleaned, and free from all traces of fat. If the blood-clot does not spontaneously retract it must be freed from the side of the glass with a flat instrument like a paper-knife without injuring it. If no clot occurs in the cold, a result may perhaps follow at blood temperature. In spite however of all artifices and all care, it is here and there, under pathological conditions, impossible to obtain even a trace of serum from considerable amounts of blood. In a horse for example which was immunised against diphtheria, and had before yielded an unusually large quantity of serum, Ehrlich was able to obtain from 22 kg. of blood scarcely 100 cc. serum, when the animal was bled on account of a tetanus infection.