Place in the Parva Naturalia In comparison to the first five treatises of the
Parva Naturalia, this one and
On Length and Shortness of Life, while still dealing with natural phenomena involving the body and the soul, are "definitely biological rather than psychological." They are omitted from the
Parva Naturalia commentary of
Sophonias.
Title and divisions of the treatise Modern editions divide the treatise into 27 chapters. The
Bekker edition of
Aristotle's works distinguished two works,
De Senectute et Juventute (chapters 1-6), and
De Respiratione (chapters 7-27, for this reason sometimes cited as
De Respiratione, chapters 1-21). However, the manuscripts give no basis for this distinction, and the contents are not accurately described by these labels; youth and old age only come into focus as "part of the explanation of life as a whole" in chapter 24. The work may, instead, be considered as a single, unified treatise on life, death, and the functions necessary to life: nutrition and respiration. The title
On Youth, Old Age, Life and Death, and Respiration, given in the Medieval manuscripts, derives from the treatise's opening words: "We must now treat of youth and old age and life and death. We must probably also at the same time state the causes of respiration as well, since in some cases living and the reverse depend on this." This statement explains how respiration is part of the more general subject of life and death. While
De Vita et Morte might, then, seem to be a more satisfactory title for the work (and
Ptolemy Chennus refers to the whole in this way), youth and old age are important aspects of the subject, because Aristotle's conception "is not of a constant, unvarying life" but of a life-cycle of natural development and decay. The motivation for this "disappointing feature of Aristotle's physiology" is a matter of conjecture; the importance of the
brain had been suggested before Aristotle by
Alcmaeon of Croton (on the basis of "the fact...that the end-organs of smell and sight are connected with the brain," with which Aristotle was familiar), and this had been accepted in turn by
Diogenes of Apollonia,
Democritus, and
Plato.
The life-cycle Chapter 24 of the treatise gives several definitions that summarize Aristotle's theory.
Respiration Respiration is the process by which breathing helps to cool and moderate the inner vital heat (
thermotēta psychikēs) held in the heart. "We have said before that life and the possession of heat depend upon some degree of heat; for digestion, by which animals assimilate their food, cannot take place apart from the soul and heat; for all food is rendered digestible by fire." 474a25-27. Aristotle explains that if there is an excess of heat created in the heart the animal will "burn out" by excessively consuming the power sustaining its life (474b10-24). Its heat must be kindled (474b13) and in order to preserve (sōtērias) life, a cooling must take place (
katapsyxis) (474b23). While all animals need both food and cooling (476a16), only those with lungs require breathing. Fish and insects cool by different means (e.g. gills or buzzing). Fish use the water to cool, and this occurs in the gills, Aristotle thinks (478a34). "animals higher in the scale of creation have more heat...they must at the same time have a higher form of soul, so they have a higher nature than that of fish." 477a18. Aristotle also says that warmer animals require more cooling (478a23). ==Commentaries==