A critical study of the direct method of measuring the osmotic pressure of hœmoglobin

Abstract

Abstract A solution of hœmoglobin and salts may be considered as a colloidal system. Since the work of Thomas Graham, it has been recognized that such systems are unstable, for they are liable to undergo gradual changes in their state of aggregation. When the chief colloid is a protein, there may be in addition actual chemical breakdown. When, the chemical instability is associated with the lag normal to the colloidal state the application of the direct osmometric method becomes peculiarly difficult, because, if the experimenter elects to wait for the system to obtain equilibrium he is likely to encounter chemical breakdown, and if he accepts the first approximately steady readings and relies upon extrapolation to give the absolute values, his conclusions can never have the finality which would alone justify the use of so difficult a method. These disadvantages can be partly met by using osmometers designed to reach equilibrium rapidly (see Section 4), but they can be wholly overcome only by discovering conditions which ensure chemical stability. Of these the most important is a low temperature, and therefore all the critical measurements described in this paper and the papers which follow were made at 0° C.