For these methods various diluting fluids are used, such as physiological saline solution, 2.5% of potassium bichromate and many others. According to H. Koeppe they are not indifferent as far as the volume of the red blood corpuscles is concerned; and a solution which does not affect the cells must be previously ascertained for each specimen of blood. For this reason attention may be called to the proceeding of M. Herz, in which the clotting of the blood in the pipette is prevented by rendering the walls absolutely smooth by the application of cod-liver oil. Koeppe has slightly varied this method; he fills his handily constructed pipette, very carefully cleaned, with cedar wood oil, and sucks up the blood, as it comes from the fingerprick into the filled pipette. The blood displaces the oil, and as it only comes into contact with perfectly smooth surfaces, it remains fluid. By means of a centrifugal machine, of which he has constructed a very convenient variation, the oil as the lighter body is completely removed from the blood; and the plasma is also separated from the corpuscles. Three sharply defined layers are then visible, the layer of oil above, the plasma layer, and the layer of the red blood corpuscles. In as much as the apparatus is calibrated, the relation between the volumes of the plasma and corpuscles can be read off. No microscopical alterations in the corpuscles are to be observed. 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 haemoglobin are by no means constant, is well shewn by conditions (for example the acute anaemias) in which an "acute swelling" of the individual red discs occurs (M. Herz), but without a corresponding increase in haemoglobin. 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.