CHAPTER X.
DISEASE.

Preliminary Problem.-Data.-Trustworthiness of R.F.F. Data.-Mixture of Inheritances.-CONSUMPTION : General Remarks ; Parent to Child ; Distribution of Fraternities ; . Severely Tainted Fraternities ; Consnmptivity.-Data for Hereditary Diseases.

THE vital statistics of a population are those of a vast army marching rank behind rank, across the treacherous table-land of life. Some of its members. drop out of sight at every step, and a new rank is ever rising up to take the place vacated by the rank that preceded it, and which has already moved on. The population retains its peculiarities although the elements of which it is composed are never stationary, neither are the same individuals present at any two successive epochs. In these respects, a population may be compared to a cloud that seems to repose in calm upon a mountain plateau, while a gale of wind is blowing over it. The outline of the cloud remains unchanged, although its elements are in violent movement and in a condition of perpetual destruction and renewal. The