The same faculty to be proved _a posteriori_. Its corresponding _function_ (_i.e._ the activation of this faculty or potentiality) well seen in the large hollow organs, notably the uterus and stomach. Chapter III Exercise of the retentive faculty particularly well seen in the uterus. Its object is to allow the embryo to attain full development; this being completed, a new faculty--the expulsive--hitherto quiescent, comes into play. Characteristic signs and symptoms of pregnancy. Tight grip of uterus on growing embryo, and accurate closure of os uteri during operation of the retentive faculty. Dilatation of os and expulsive activities of uterus at full term, or when foetus dies. Prolapse from undue exercise of this faculty. _Rôle_ of the midwife. Accessory muscles in parturition. Chapter IV Same two faculties seen in stomach. _Gurglings_ or _borborygmi_ show that this organ is weak and is not gripping its contents tightly enough. Undue delay of food in a weak stomach proved not to be due to narrowness of pylorus: length of stay depends on whether _digestion_ (another instance of the characteristically vital process of _alteration_) has taken place or not. Erasistratus wrong in attributing digestion merely to the mechanical action of the stomach walls. When digestion completed, then pylorus opens and allows contents to pass downwards, just as os uteri when development of embyro completed. Chapter V If attraction and elimination always proceeded _pari passu_, the content of these hollow organs (including gall-bladder and urinary bladder) would never vary in amount. A _retentive_ faculty, therefore, also logically needed. Its existence demonstrated. Expulsion determined by qualitative and quantitative changes of contents. "Diarrhoea" of stomach. Vomiting. Chapter VI Every organic part has an _appetite_ and _aversion_ for the qualities which are appropriate and foreign to it respectively. Attraction necessarily leads to a certain _benefit_ received. This again necessitates _retention_. Chapter VII