Perhaps a larger _role_ is to be allotted in the diseases of the blood to these conditions. Hayem already turns the incomplete production of serum to account, for distinguishing protopathic pernicious anaemia from other severe anaemic conditions. A bad prognosis too may be made when for example in cachetic states this phenomenon is to be observed. A few methods still remain to be mentioned which test THE RESISTANCE OF THE RED BLOOD CORPUSCLES to external injuries of various kinds. Landois, Hamburger and v. Limbeck ascertain for instance the degree of concentration of a salt solution, in which the red corpuscles are preserved ("isotonic concentration," Hamburger) and those which cause an exit of the haemoglobin from the stroma. The erythrocytes are the more resistant, the weaker the concentration which leaves them still uninjured. Laker tests the red blood corpuscles as regards their resistance to the electric discharge from a Leyden jar, and measures it by the number of discharges up to which the blood in question remains uninjured. Clinical observation has not yet gained much by these methods. So much only is certain, that in certain diseases: anaemia, haemoglobinuria, and after many intoxications, the resistance, as measured by the methods above indicated, is considerably lowered. FOOTNOTES: [1] For the estimation of the numbers of white corpuscles, relatively to the red, and of the different kinds relatively to each other, see the section on the morphology. [2] In Roy's method, mixtures of glycerine and water are used. By means of a curved pipette, the drop of blood is brought into the fluid, and its immediate motion observed. Lazarus Barlow has modified this method. He employs mixtures of gum and water, and instead of several tubes, one only; and into this the mixtures are introduced, those of higher specific gravity being naturally at the bottom. The alternate layers are coloured, and remain distinguishable for several hours. [3] In conditions of shock experimentally produced, the specific gravity of the total blood is increased, that of the plasma, however, is diminished (Roy and Cobbett). THE MORPHOLOGY OF THE BLOOD. A. METHODS OF INVESTIGATION.