The ethnic stream may start comparatively pure, but it becomes mixed on the way.

From time to time it leaves behind laggard elements which in turn make a new racial blend where they stop.

Such were the six thousand Aduatici whom Caesar found in Belgian Gaul.

These were a detachment of the migrating Cimbri, left there in charge of surplus cattle and baggage while the main body went on to Italy.[142] [Sidenote: Complex currents of migration.] A migration rarely involves a single people even at the start.

It becomes contagious either by example or by the subjection of several neighboring tribes to the same impelling force, by reason of which all start at or near the same time.