If, then, heat plays so important a part in abnormal functioning, so must it also in normal (_i.e._ causes of eucrasia involved in those of dyscrasia, of physiology in those of pathology). A like argument explains the _genesis of the humours_. Addition of warmth to things already warm makes them bitter; thus honey turns to bile in people who are already warm; where warmth deficient, as in old people, it turns to useful blood. This is a proof that bile does not pre-exist, as such, in the food. Chapter IX The _functions of organs_ also depend on the way in which the four qualities are mixed--_e.g._ the contracting function of the stomach. Treatment only possible when we know the _causes_ of errors of function. The Erasistrateans practically Empiricists in this respect. On an appreciation of the meaning of a _dyscrasia_ follows naturally the Hippocratic principle of treating opposites by opposites (_e.g._ cooling the over-heated stomach, warming it when chilled, etc.). Useless in treatment to know merely the function of each organ; we must know the _bodily condition_ which upsets this function. Blood is warm and moist. Yellow bile is warm and (virtually, though not apparently) dry. Phlegm is cold and moist. The fourth possible combination (cold and dry) is represented by _black bile_. For the clearing out of this humour from the blood, Nature has provided the spleen--an organ which, according to Erasistratus, fulfils no purpose. Proof of the importance of the spleen is the jaundice, toxaemia, etc., occurring when it is diseased. Erasistratus's failure to mention the views of leading authorities on this organ shows the hopelessness of his position. The Hippocratic view has now been demonstrated deductively and inductively. The classical view as to the generation of the humours. Normal and pathological forms of yellow and black bile. Part played by the _innate heat_ in their production. Other kinds of bile are merely transition-stages between these extreme types. Abnormal forms removed by liver and spleen respectively. Phlegm, however, does not need a special excretory organ, as it can undergo entire metabolism in the body. Need for studying the works of the Ancients carefully, in order to reach a proper understanding of this subject. BOOK III Chapter I A recapitulation of certain points previously demonstrated. Every part of the animal has an attractive and an alterative (assimilative) faculty; it attracts the nutrient juice which is proper to it. Assimilation is preceded by adhesion (_prosphysis_) and that again, by application (_prosthesis_). Application the goal of attraction. It would not, however, be followed by adhesion and assimilation if each part did not also possess a faculty for _retaining in position_ the nutriment which has been applied. _A priori_ necessity for this _retentive_ faculty. Chapter II