We may trace the inflow of country-born people into the towns by looking either at the statistics of towns, or of rural districts. But first we ought to bear in mind one fact. Quite apart from any change in proportion of population, there is an enormous interchange constantly taking place between adjoining counties and districts. The general fluidity of population has been of course vastly increased by new facilities of communication and migration; persons are less and less bound down to the village or county in which they were born. So we find that in England and Wales, only 739 out of each 1000 persons were living in their native county in 1901. In some London districts it is reckoned that more than one quarter of the inhabitants change their address each year. So that when we are told that in seven large Scotch towns only 524 out of each 1000 are natives, and that in Middlesex only 35 per cent. of the male adult population are Middlesex by birth, we are not thereby enabled to form any conclusion as to the growth of towns. To arrive at any useful result we must compare the inflow with the outflow. Most of the valuable information we possess on this point applies directly to London but the same forces which are operating in London, will be found to be at work with more or less intensity in other centres of population in proportion to their size. Comparing the inflow of London with its outflow, we find that in 1881 nearly twice as many strangers were living in London as Londoners were living outside; in other words, that London was gaining from the country at the rate of more than 10,000 per annum. So far as London itself is concerned, the last two censuses show a cessation of the flow, but the enormous growth of Middlesex outside the metropolitan boundaries indicates a continuance of the centripetal tendency. Now what does London do with this increase? Is it spread evenly over the surface of the great city? Certainly not. And here we reach a point which has a great significance for those interested in East London. It is clearly shown that none of this gain goes to swell the numbers of East London. Many individual strangers of course go there, but the outflow from East London towards the suburban parts more than compensates the inflow. By comparing the population of East London in 1901 with that in 1881, it is found that the increase is far less than it ought to be, if we add the excess of births over deaths. How is this? The answer is not far to seek, and stamps with fatal significance one aspect of Poverty, namely, overcrowding. East London does not gain so fast as other parts, because it will not hold any more people. It has reached what is termed "saturation point." Introduce strangers, and they can only stay on condition that they push out, and take the place of, earlier residents.