But, in addition to this, fundamental problems in the chemistry of large molecules are to a high degree dependent on the development of suitable and highly specific separation methods. Thus, the problem of separation is of the utmost interest far beyond preparative aspects, and can often supply important information about the existence of biochemically significant complexes, for example between a prosthetic group and a protein in an enzyme. I particularly wish to emphasize that the definition of a chemical entity, which just in this particular field is often extremely difficult, ultimately depends on the separa-tion methods we have at our disposal, or those which are thought to be suitable for use without danger of altering the substance in question. certain enzymes) and also to define 196 1948 A.W.K.TISELIUS and characterize these substances as accurately as possible. In these branches of bio-chemistry some of the most important problems are to isolate the substances which are responsible for a specific biological or biochemical effect (e.g. Such is the case when he works with substances belonging to the common organic substances of more or less known structure, and is true to an even greater extent if he is in-terested in complex substances of large molecular weight, for example: pro-teins, enzymes, viruses, polysaccharides, and nucleic acids, whose detailed structure is as yet unknown, but which on account of their great significance in fundamental life processes are objects of especially intensive study at present. Almost daily the biochemist is faced with separation problems in his laboratory.

Separation methods for preparative and analytical purposes are, as is well known, of fundamental importance in the chemists' work, It is illuminating that in the Dutch language 'Scheikunde' or the Art of Separation, is even today often used as a name for chemistry. Fundamentally, the significance of these methods up to the present time lies in the opportunities which they offer for making use of these phenomena for a rational separation of substances in solution under conditions which are especially favourable to many substances of biochemical significance.

Electrophoresis and especially adsorption would not, however, have come to play their present roll in chemistry if they had only been utilized for the characterization of different substances. These phenomena are specific in the sense that they often display wide variation from substance to sub-stance and therefore are well adapted for the characterization of certain sub-stances which are otherwise difficult to define like proteins and other bio-colloids. The methods, whose development and use I shall attempt to describe in this lecture, have a common characteristic: they are based on certain specific physico-chemical properties of the substances to be studied, namely, their migration in an electric field (electrophoresis) or their affinity to the surface of a finely divided solid substance (adsorption).

Macvector video