The term ''diathesis'' is applied to an inherited predisposition to alterations of nutrition. Nutrition consists of the transformation of non-living molecules into living cells (assimilation) which undergo chemic changes with oxygen (reaction), producing waste material that in time is thrown off to make room for fresh cells (disassimilation). Nutrition is controlled by the nervous system, and is modified by age, sex, climate, food, geographic and geologic position, occupations, manners and customs, hygienic conditions, variations of light, heat, moisture and atmosphere (environment). Continuous subjection to any of these conditions modifying nutrition becomes apparent in the progeny of individuals; and this functional alteration of nutrition, causes a predisposition to pathologic conditions, or a pathologic condition itself, known as diathesis.
Bouchard defines ''constitution'' as including all that is concerned with the structure and framework of the body; while the word "temperament" includes everything that pertains to the individual characteristics and functional activity. Constitution