68 THE AMERICAN JOURNAL OF SOCIOLOGY
and also for peaceful agreements. It is thus in organisms; the nervous system and the special organs of sensibility are formed from the outside cells, those directly in contact with excitations from without.
The social frontiers appear to us, then, as the resultant of a continual but changing equilibration between the internal molec- ular composition of each social group, on the one hand, and of the external and equally molecular composition of the groups, on the other, whence come molar action and reaction; that is, inter-group, the result of which is a reciprocal limitation, an inter-group equilibrium, the first manifestation of which is a boundary, placed just where the equilibrium is produced. And here appears the positive role of the frontier, which has been represented, up to this time, only as a negative function, that of obstacle, of separation, more or less insurmountable. This nega- tive function is, in reality $ entirely secondary. The constant and positive function of every frontier is to bring together the internal forces of a society and the forces of external groups, and, in a general way, put them in equilibrium. The frontier is above all the organ of movements and inter-group exchanges, the organ of the life of the relation between the groups, a regis- ter and a monitor, which informs the group continually concern- ing its possible expansion and upon its necessary contractions.
Up to this time, the social relations having been developed chiefly under military form, and all the internal structure of society having received the imprint of that form, the frontiers have been equally conceived and established with the same point of view. But conquest and war are rude and abominable forms of relation between nations; and this is precisely what explains why the limits have always been changing, and why, in reality, the limits, called natural, have themselves always been over- stepped, by virtue of the constant and universal law which pro- portions the extension of each group to its composition and to its internal organization as related to the same conditions among neighboring groups.
In that constant and always unstable equilibrium the consid- eration of the exterior group and of the purely physical sur-
