OUR NATURAL INHERITANCE 75 



and to distinguish it from symptoms of an early in- 

 fection already accomplished. 



(d) The boundary-line between health and disease 

 is not readily drawn, but from the biologist's point of 

 view disease means that certain vital processes (or 

 metaboHsms) are occurring out of place, out of time, 

 or out of tune. This disturbance of the wholesome 

 routine may be traced back and back to some disturb- 

 ance in the organisation and activity of the original 

 germ-cells. Such diseases are called constitutional or 

 innate, and they or predispositions to them may be 

 transmitted from generation to generation in Man's 

 sheltered kingdom. In wild nature they are not allowed 

 to grip. In illustration of such diseased conditions we 

 may mention diabetes (D), epilepsy (R), feeble-minded- 

 ness (R), glaucoma (D). These follow the Mendelian 

 rule. They are marked (D) or (R) according as they 

 happen to be dominant or recessive in relation to nor- 

 mality. 



(e) There are other diseased conditions, however, 

 which are directly induced by deteriorative peculiarities 

 in surroundings, food, occupation, habits, and the like. 

 Such might well be called modificational diseases, e.g. 

 the conditions brought about by white-lead poisoning, 

 by over-indulgence in alcohol, by working under great 

 atmospheric pressure, and so on. If the disease called 

 beri-beri be due, as experts tell us, to lack of ' vitamines ' 

 in the food, e.g. to feeding almost exclusively on polished 

 rice from which the rind has been removed, then it is 

 a good example of a modificational disease. Now the 



