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 ; Con- 

 sumptivity. — 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 popu- 

 lation 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 com- 

 pared 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 



