A photoelectric instrument for comparing the concentrations of very dilute aerosols, and measuring low light intensities.

The observed mobility ranges for the chief electrophoretic components of plasma and its fractions, as studied under conditions standard for control of large-scale fractionation, fall into two classes : (1) components poor in lipoids, whose characteristic mobilities appear independent of conditions of fractionation, degree of purity and usual conditions and duration of storage; ( 2 ) components rich in lipoid whose characteristic mobilities vary with these factors, generally toward increasing negativity, thus yielding overlaps of mobility range with components of the first class. The small variations of apparent electrophoretic distributions of normal human plasma pools under standard analytical conditions is indicated in a series of analyses carried out over a period of years in potassium phosphate a t PH 7.7 and sodium diethylbarbiturate a t pH 8.6. Comparisons with apparent distributions in other buffers less useful for fractionation control are given. Specific refractive index increments of electrophoretically separated albumin and 7-globulin have been found to approach with increasing electrophoretic homogeneity the increments for these components as separated chemically. Conversion factors (based on refractive index increments in terms of weight of dried protein) have been computed for the chief electrophoretic components in plasma and the major fractions. When applied, together with corrections based on nitrogen factor differences and on deviations of apparent distributions from true relative concentrations in mixture studies, in revision of schlieren data for a second approximation of the distribution of components in plasma and fractions, the internal consistency of .the results has proved little better than when unrevised apparent distributions obtained under standard conditions are used. Two factors appear chiefly responsible: uncertainties in diagram resolutions of components comprising molecular species of considerable mobility spread, together with changes of apparent distributions resulting from slight mobility changes with processing. The principal value of the electrophoretic method in the control of fractionation has been its use in quantitative first approximation: (a) for revealing gross differences of apparent distributions with variation in conditions of fraction separation, and (b) as a rapid empirical control of uniformity of successive separations under constant conditions. Specialized indications for the use of corrected electrophoretic diagrams in clinical and biological investigation are given.