The introduction to the first of these two volumes on Charged Gels and Membranes has recalled already that both were issued from the second Advanced Study Institute of Forges les Eaux, of which the co-directors were Professors G. E. Boyd and K. S. Spiegler. However, it seems necessary to add some further remarks for the eventual readers of this one volume only or for those of all four which now constitute the series. * One discovers that each volume is precisely linked to the next; and the total con­ tains a large number of the very fundamental steps by which macromolecular physical chemistry finds itself simultaneously at thefronNers of application and of biology. One often wonders how this is possible. Research has been the best means of unders~anding the microscopic elements oflife. Biomimetic phenomena or bioanalogue compounds in their turn have led to innumerable practical realisations. On one hand, the notion of 'vital force' receded and is disap­ pearing due to repetitive total and asymmetric synthesis* of always larger, and more complex, biological molecules. On the other hand discoveries of inter-relations in physical chemistry disengage the analogies between living and non-living systems: the interrelations between phenomena, between phenomena and structures or the appear­ ance of these structures under the influence of intermolecular forces or of gradients of more statistical forces.