THE FINAL SYSTEM! GALEN present the working of the innate attractive and alterative powers of the organs, whereby they take and transform whatever nutriment is needed for their functions. Galen writes as a physiologist or biologist^ though he has in mind the medical usefulness of his matter. The opening paragraph of the third book gives his final summary of this subject: " It has been made clear in the preceding discussion that nutrition occurs by an altera- tion or assimilation of that which nourishes to that which receives nourishment, and that there exists in every part of the animal a faculty which in view of its activity we call, in general terms, alterative, or, more specifically, assimilative and nutritive. It was also shown that a sufficient supply of the matter which the part being nourished makes into nutriment for itself, is ensured by virtue of another faculty which naturally attracts its proper juice [humour] ; that that juice is proper to each part which is adapted for assimilation, and that the faculty which attracts the juice is called, by reason of its activity, attractive or epispastic. It has also been shown that assimi- lation is preceded by adhesion, and this, again, by presentation, the latter stage being, as one
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