Then, too, we know from this that the true function of breathing is to bring enough fresh air into the lungs to cause the blood entering them from the right cavity into the heart, where it has been rarefied and, as it were, changed into vapour, to thicken up and convert itself once more into blood, before falling back into the left cavity; if it did not do this, it would not be fit to nourish the fire that is there. All this is confirmed by the fact that we see that animals not having lungs have also only one cavity in the heart, and that unborn children, who cannot use their lungs while in
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cardiovascular physiology a la Descartes
