The methods of protein fractionation based on physical differences between the various fractions are peculiarly suitable for the identification and isolation of active protein principles. Even mild chemical treatment, such as precipitation with alcohol, appears at times to denature the active protein principle. In electrophoresis proteins are fractionated according to their rate of movement in an electrical field; this is dependent on the charge on the protein molecule and on its size and shape. In this procedure serum proteins are divided into the principal fractions: albumin; alpha, beta and gamma globulins, and fibrinogen.
The fractions obtained by electrophoresis, however, should not be considered to be chemically homogeneous without additional evidence, such as chemical analysis, crystallization, ultracentrifugal analysis and, perhaps