1. An analysis by the “generation mortality” method of the specific mortality rates of the urban and rural areas of Scotland for various calendar periods from 1871 onwards shows that the “diagonal law” previously demonstrated for the population of Scotland as a whole, as well as for certain other European countries, holds for these two subdivisions of the community.

2. Reasons are given for the assumption that the normalized “generation mortality coefficients” (α values) may be taken as a rough measure of the “healthiness” of the environmental conditions which obtained during the childhood of the generation to which they refer. This affords a basis for the comparison of the “healthiness” of the environment of town and country at different periods in the past.

3. Whereas in the earlier half of the nineteenth century the ratio of the α values of country to town was in the neighbourhood of 0·6, indicating that the health conditions in the country might be said to be almost twice as good as in the towns, in 1931 it had risen to almost unity, showing that by that time the town had almost if not quite made up on the country. During this period both town and country conditions showed remarkable improvements, which are reflected in falls of the respective α (× 1000) values in the country from about 12 and in the town from over 20 in 1841, to a common level of about 4·7 in 1931.

4. The essential vagueness of the conception of the “healthiness” of an environment is emphasized. It is consequently necessary not to attach too great importance to the estimate of the date, but the figures given in Table 5 confirm the conclusion that, as regards “healthiness”, between 1930 and 1935 conditions in town and country had become nearly equal.