Though this procedure seems very difficult of execution, it is nevertheless the only one, which has really advanced clinical pathology. The results of Koeppe--not as yet very numerous--give the total volume of the red corpuscles as 51.1-54.8%, an average of 52.6%.
M. and L. Bleibtreu have endeavoured indirectly to ascertain the relation of the volume of the corpuscles to that of the plasma. Mixtures of blood with physiological saline solution in various proportions are made, in each the amount of nitrogen in the fluid which is left after the corpuscles have settled is estimated. With the aid of quantities so obtained they calculate mathematically the volume of the serum and corpuscles respectively. Apart from the fact that a dilution with salt solution is also here involved, this method is too complicated and requires amounts of blood too large for clinical purposes. Th. Pfeiffer has tried to introduce it clinically in suitable cases, but has not so far succeeded in obtaining definite results. That, however, the relations between the relative volume of the red corpuscles and quantity of hæmoglobin are by no means constant, is well shewn by conditions (for example the acute anæmias) in which an "acute swelling" of the individual red discs occurs (M. Herz), but without a corresponding increase in hæmoglobin. The same conclusion results from recent observations of v. Limbeck, that in catarrhal jaundice a considerable increase of volume of the red blood corpuscles comes to pass under the influence of the salts of the bile acids.
As we have several times insisted, the quantity of hæmoglobin affords the most important measure of the severity of an anæmic condition. Those methods which neither directly nor indirectly give an indication of the amount of hæmoglobin 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 hæmorrhagic 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.