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.
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.
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.
[3] Aristotle's account of the heart provides one of the clearest indications that he was familiar with the medical theories of some parts of the Hippocratic Corpus.
[3] That is, the heart ("hot substance" in animals) is inside the lungs ("the primary organ of cooling," a function also served by gills); the heart expands under the influence of heat, forcing the lungs to expand under the same influence, causing inhalation, and this introduction of cold air from outside in turn causes contraction and exhalation.
[5] Respiration is the process by which breathing helps to cool and moderate the inner vital heat (thermotēta psychikēs) held in the heart.